Re: 8350B w/83590A repair advice
On Mon, 16 Dec 2019, victor.silva via Groups.Io wrote: Tried to send direct without looking at the header so it bounced... Sorry for posting to the list but it won't go otherwise. Here is the original message: === Cut === It looks like Paul Bicknell asked for that one first but if he didn't buy it you can get it. I took some pictures minutes ago, they are available at It is a 44+ MBytes archive with several photos. === Cut === Sergey,
I would be interested in the 83570A.
I agree with your recommendation for removing the battery.? I did that to
mine 8 years ago and have not regretted it.
--Victor --- * * KSI@home KOI8 Net < > The impossible we do immediately. * * Las Vegas NV, USA < > Miracles require 24-hour notice. * *
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Re: Help to repair my HP654A Test Oscillator
Maybe mine needs a similar fix.? I will look at it one of these days.? Low distortion is important.
Bob
On Monday, December 16, 2019, 02:34:28 PM PST, Marco Marchesi <marco.marchesi@...> wrote:
Hi. GOT IT!
There was a ground loop gathering noise and hum.?
I moved the ground connection of the third gang of the variabile Cap in the same point where Wien bridge resistive leg is grounded.
Now I got -50,1 dB THD @ 1 KHz, -10 dB under spec.
I'm really happy.
Thank you!
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Re: Help to repair my HP654A Test Oscillator
Hi. GOT IT!
There was a ground loop gathering noise and hum.?
I moved the ground connection of the third gang of the variabile Cap in the same point where Wien bridge resistive leg is grounded.
Now I got -50,1 dB THD @ 1 KHz, -10 dB under spec.
I'm really happy.
Thank you!
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Re: OT? Comb mixer, drive level?
Hello,
Yes, this is the input receiver section where RF is down converted to somewhere around 25 - 270 MHz to fit the second mixer, which brings it to exactly 2.5 MHz.
I have tried to feed the output of the PA through an attenuator, but it does appear as if the mixer needs full power. I have attached a picture of the board and a measurement of saturated output (input power of 5 dBm, seems like the level from the VNA also). The instrument seems to lock for any LO setting below approximately - say - 520 MHz so the following mixer appears to be working. The bad thing is that during a sweep, the higher LO frequencies appear and then the VNA gets stuck. Needless to say, the higher RF makes more use of higher LO frequencies...
Anyone knows of a good amp that provides 30 dBm _flat_ between 360 and 540 MHz??
Or, any suggestions on how to trim the current amp to give those final dBm at the higher range?
Perhaps the step recovery diode isn't properly matched right now - there is a PI net of caps and a trim pot at the output. They are set as they were from the beginning. The problem is however that it is almost impossible to trim the unit when it is installed (the lid is holding the amp). My guess is that a generic tuning is sufficient and it seems like the output power curve well matches how well the mixer works.
It's great to see that it now locks also at high RF, but frustrating that it won't run a full sweep. Should perhaps rewrite the code to only use frequencies below 500 MHz?... Not likely...
Sad thing with Wiltron is that any technical documentation at the level where HP provided is nearly nonexistent. PLEASE anyone, PROVE ME WRONG!
Regards,
? Staffan
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Re: 8350B w/83590A repair advice
Sergey,
I would be interested in the 83570A.
I agree with your recommendation for removing the battery.? I did that to mine 8 years ago and have not regretted it.
--Victor
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Re: Wanted: HP 3458a DVM in non-working condition
I agree with that. A few years ago 3458As with issue would go for $1500, I even saw some under a thousand.
Lately they are all over $2000, for example the unit mentioned on ebay in this thread, went for?$2,222.22.
It was an older unit, but did have option 002 (and 001).
The problem with trying to get a dead but complete unit is that a dead unit draws a lot of attention.
P/S issues are usually the easiest to diagnose and fix (IMHO), so I think those units draw attention from people hoping for an easy score.
--Victor
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Ok, I think I can answer my first question. The CRC with additional Rs to ground is DC blocking capacitors either side of a pi-pad attenuator. Given the 300 and 18 ohm resistance, they're just about 3dB with 50Ohm impedance. This means that the input LO has 2x20dB of gain from the SBB5089Z as well as 3x-3dB of attenuation from the pi-pad attenuators, so overall 31dB of gain, lifting my input LO from -12 to +19dB into the mixer (ignoring other insertion losses). The absolute maximum rating for the mixer is 13dBm for the RF in, so this seems plenty of power to work with the mixer. I will check what level the voltage controlled attenuator is being driven to.
Happy to hear suggestions on the RF side, my RF knowledge is still quite weak.
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Re: 2401C Integrating Digital Voltmeter and 2410B AC - Ohms Converter
On 12/16/19 3:40 AM, Terry Gains wrote: I have a old, much-used 2410B manual to work from, but will get a new
one to make the job easier. Any idea if that manual has been scanned? A quick Google doesn't turn it up anywhere. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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Re: Wanted: HP 3458a DVM in non-working condition
Out of curiosity quick scan on ebay:
1 pc NOT working HP 3458A Multi-meter "For parts or not working"
Already at $2.132, 12 minutes to close.
Not related in any way to the auction.
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As promised, here's an update on adding a LO port and external tracking generator for the 8591A. The output of the (originally terminated) TG LO port on the first mixer is about -12dB once I routed it out of the back of the unit, but its exactly in the right frequency range. I bought the BG7TBL 2017-11-26 tracking generator, connected it but its not working. Borrowing a second spectrum analyser, I can see that the TG signal is 400 MHz lower than the monitored frequency of the 8591A, so its working but the frequency of the LO in the TG is 400MHz is too low. No problem, that's what the front "Freq. Adj." is for right? Wrong, it only allows for a change in frequency of about 30kHz, so its for fine tuning only. I check my order, and it turns out I bought the TG for the Anritsu MS610 as it saved me about ?20, and sure enough, the difference between the MS610 and the 8591A first converter IFs is 400MHz. That ?20 is starting to look worthwhile now. I also note that the max output of the TG is -20dB. Again, there's a "Lev. Adj." dial on the front, but this only changes it from -40dB to -20dB and at max there's a lot of spurs at the max setting. Right now, it looks like the LO from the 8591A needs to be amplified before heading into the TG? Time to tear the TG down and see how I can adapt it to work for the 8591A by changing the oscillator frequency. Here's a picture of the insides:  There's an ATMega8 which seems to control the PLL hidden under the small RF shield, while the actual mixing etc seems to be under the larger shield. Its well laid out but the front pots/knobs are really cheap. Its a two layer board too, but the underside is nearly an unbroken ground plane. The only exception are some very short jumpers to the other side underneath the RF shields, mainly for the digital signal lines. Soldering quality seems good with some small bodge jobs here and there. The large RF shield only had one soldered tab and the others were just bent so it was easy to remove. The PLL shield was a horror to remove.?  ? The LO input comes through two stages of amplification using two (+20dbm 0-4GHz), before hitting the ?(1.5-4.5GHz RF/LO input, DC-1.5GHz output), so its specified output freq. range is a little below the range of the 8591A. This seems to be plenty of gain for the LO input, so maybe there's some attenuation to provide isolation? The PLL is a (137.5 MHz-4.4GHz), driven by a three wire SPI-like interface from the ATmega8a in the bottom right. This is then attenuated using a voltage-controlled?attenuator before again being buffered by an SBB5089Z before entering the . After the mixer there's two unknown chips (filters?) labelled F1 and F2, before another SBB5089Z, then some kind of detector(?)/power-splitter before entering into the LM358 op amp, which I think must be comparing against the potentiometer as its output goes into the control pin of the AT-108 attenuator, thus I'm guessing its the level control. The on-board pots are "overridden" by the front panel pots and do nothing while they are attached so I think the board is designed to run stand-alone from the case. Strange that they're populated anyway. There's no serial output from the ATMega, despite the on-board RX/TX connector in the bottom right, but I'm guessing this is how the PLL frequency is varied/programmed between the different units sold.? My next step is to trace out the ATmega8a connections to see if its just controlling the PLL, then record the exact commands sent to the PLL, then reprogram the ATmega8 to send a command with a frequency 400MHz higher. If this works, I'll look at adding a display interface to the ATmega to allow a controllable frequency offset for offset sweeps and maybe other fun ideas. Let me know if you want any more information on this tracking generator, I'll update again once my AVR programmer has arrived and I've scoped out everything that its doing. I have two questions. Between the SBB5089Z there's often a CRC component with R=18Ohms, and two 300Ohm grounding resistors either side of it. I understand the need for the C, as its blocking the DC bias for the SBB5089Z, but not why the resistors are there. Is it for attenuation to provide isolation? Its not a matching circuit as everything is internally matched to 50Ohm. There's even a case where its not used, i.e. from the PLL to the mixer. The second question is any ideas why the two stages of +20dB gain each are not enough for the input LO? Is it because those resistors are indeed there for attenuation? I've bought a cheap RF amplifier module off amazon, I'm hoping just adding this to the LO input will bring up the amplitude of the TG output. Thanks!?
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Re: 2401C Integrating Digital Voltmeter and 2410B AC - Ohms Converter
I guess whichever of us gets the time to do the boards will then have to share with the other.??
You bet. There are many crowds that can make the PCBs with cut outs and edge connectors etc. For example the work could be sent to?although they will probably squawk when I ask for "Gold PCB tracks". :) I have a old, much-used 2410B manual to work from, but will get a new one to make the job easier. Kind regards, Terry
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Re: 2401C Integrating Digital Voltmeter and 2410B AC - Ohms Converter
Hi Pat,
The trick about using eBay for rare items is to set your search to world wide. I learned this the hard way after missing out on a 3461A AC/Ohms Converter, DC-Preamplifier?the was sold on Ebay in Hamburg in March last year..........for less than $100 USD. You could have knocked me over with a feather when I found out the price.
This was the 2nd?3461A?I had seen sold in Europe in the last 5 years, which gives me hope that there are more out there.
I'm getting on in years now but If ever I purchase a 3461A, it's good to know I can pass on ownership one of the many fine folk of this group.
Images are attached with a small PDF.
When connected to the 3460, it makes for a very capable and attractive looking offering from HP.
The search goes on.
Kind regards,
Terry
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Re: seeking schematic and any experienced advice FOLLOW-UP MESSAGE with correct model number
Greetings,
Thanks to Dave B and Robert G8RPI for your replies.
I will share your messages with my friend so we can figure out our next move.
Warm regards,
Ken
toggle quoted message
Show quoted text
On 15Dec, 2019, at 1:14 PM, Dave_G0WBX via Groups.Io <g8kbvdave@...> wrote:
From personal experience with that flavour of SMPS in other products.
It's more likely that the PFC front end has "blown up!"
They are fairly easy to remove the PCB's, upon which you'll easily see
the tell-tale marks of disaster.
I had one though, where one of the regulator cards had gone short-cct at
it's HVDC input, destroying itself, and taking the input card too (as
well as blowing one of the interconnect pins, like a fuse-wire!)
Like many similar things, there is a lot of current going round in
circles in those PSU's, and any compromise in cooling seems to push them
over the edge, even if the load is well within spec'.
TDK Lambda in the UK are reachable, and have a repair service, should
you need. I don't know if they have similar facilities elsewhere on the
planet, other than perhaps the far east, where a lot of the modules are
actually manufactured.
73.
Dave B.
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Re: Help to repair my HP654A Test Oscillator
We all have too many projects! I have a photo to post on the 200CD distortion subject but couldn¡¯t find anything on the web site about whether images are allowed.?
On Sun, Dec 15, 2019 at 1:51 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
Jeremy, I couldn't find anything on 200CD in EL34 website.? But the other one yielded essentially the same info as you gave on level setting.
I am resisting the temptation to get into these oscillators.? I don't have bench space and too many things going on.? But soon.
Bob
On Sunday, December 15, 2019, 01:34:00 PM PST, Jeremy Nichols < jn6wfo@...> wrote:
Matching tubes: I didn¡¯t want to repeat myself. For my 200CD, I found a matched pair of 8425A¡¯s (the industrial version of 6AU6A) for V1 and V3. (Please don¡¯t tell HP they¡¯re Tektronix tubes!) For V2 and V4 (6CW5) I found a nice pair of Made-in-Holland Amperex tubes in my spares box.?
I agree the prices on eBay are steep and that seems to be so for much older HP equipment. Clearly, sellers don¡¯t understand that the market is limited for this stuff. The ¡°sold¡± listings on eBay range from $15.50 to $150. Plus shipping, of course. Flea markets and estate sale prices are much more attractive.?
There is some good 200CD information in <> search for ¡°HP 200CD oscillator repair.¡±?
Another good link is <>. Under ¡°General Vintage Technology/Success Stories¡± search for ¡°Hewlett Packard 200CD Wide Range Oscillator.¡±
Jeremy? N6WFO
On Sun, Dec 15, 2019 at 10:35 AM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
I will have to check my serial numbers.? Your most recent message didn't mention matching tubes.
Anyway, this is interesting.? The easiest mods would be to lower the amplitude and improve the lamp sockets.? I will do those first and see what I get.? If results are promising I can get rid of the function generator.? Matching tubes can only work if both units use the same type, or I can find a source of them.? Buying tubes in hopes of finding a good match and then seeing if that helps seems a waste of effort and money.
I have two of these, one is rack mount and I don't want to preserve that one.? So I will concentrate on improving the cabinet mounted unit.
Perusing ebay shows that you can't buy a working unit for less than about $100.? I am amazed that their perceived value is that high.? Once this is done I may put one or both on ebay depending on distortion.? Of course I can brute force lower distortion with a filter but that makes for another project.
Bob K6DDX
On Sunday, December 15, 2019, 10:02:20 AM PST, Jeremy Nichols < jn6wfo@...> wrote:
*** Distortion of the HP-200CD ***
I used my HP-330B Distortion Analyzer to check the 200CD. The 330B is a vacuum tube unit; 0.04% is definitely pushing its limits; it probably would be more fair to claim my 200CD's distortion is "less than 0.1%."
*** Additional information on the HP-200CD Audio Oscillator. ***
1. The later versions using miniature tubes have lower distortion than the earlier versions with octal tubes. The split appears to have taken place at serial prefix 103, which also introduced Dynamic Balance Adjust pot R50 and Hum Balance pot R51.
2. The 200CD was listed in HP catalogs beginning in late 1951 ($150) and was last in the 1985 catalog (un-priced but I have been told it sold for $1250). This 34-year production run is probably a record for HP. The 200CD was HP's second-to-last vacuum tube instrument. One of this nice things about this long run is that there are a zillion of them still floating around for those of us who like to play with the descendants of HP's very first product.
3. The internal pot that sets the maximum output is R11 (1000 Ohms), which is normally set for a 24 Volt no-load output at 1000 Hertz (12 Volts into a 600 Ohm load). If the output is reduced below 10 Volts (loaded) the distortion is reduced; below 7.5 Volts is even better. Clearly, if your application requires higher voltage, you have to live with more distortion.
4. The manual sold by Artek (CD or download) includes in the second volume a group of HP "Service Notes" that are especially valuable for those owning early models using octal tubes. 5. The last revision appears to carry serials prefixed "960-" or "0960A." These final versions use solid-state rectifier diodes and have a standard IEC plug-in power cord.
It's interesting that the 200CD does not have a regulated power supply, only a pi-network filter.
The solid-state rectifier does not make much, if any improvement in distortion. (My "best" 200CD carries serial prefix "333-.")
6. Some excellent information, copied from the old Ampex mailing list, is posted in . This includes detailed information on the 7.5 Volt modification (which I did not do to my 200CD). 7. In the last versions, the sockets for resistor lamps RT1 and RT2 are mounted on a small pc board (with other components). Ensuring good contact between the sockets and the traces can be challenging due to the riveted construction.
Jeremy
On Sat, Dec 14, 2019 at 11:38 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
Okay Jeremy I appreciate it.? I have two 200CDs and am sure I can glean a matched pair of tubes from the four.? In any case I am interested in taking this far enough to at least approach the amount of distortion you have.? How did you measure it, and under what settings and conditions?
I have a 331A but don't use it.? A VNA I have does go down into the audio, as well as the FFT in one of my scopes and I can measure distortion that way.? I never measured anything as low as 0.04% though.
Bob K6DDX
On Saturday, December 14, 2019, 11:29:55 PM PST, Jeremy Nichols < jn6wfo@...> wrote:
There are a number of tricks that have been published over the years. I¡¯ll send you copies tomorrow. In the?meantime,? ? balance the two pairs of tubes that make up the push-pull oscillator. The pairs of tubes don¡¯t have to be new/perfect but should be as close as possible in terms of gain.? ? make sure the two lamps in the oscillator feedback have clean bases, are making tight contact with clean sockets, and the sockets have good solder connections. Sockets that are mounted with rivets to a pc board are especially susceptible to poor contact.? ? use the internal gain control (tomorrow I can give you the R-number) to reduce the maximum output to 10 Volts, perhaps even less depending on your needs. Reducing the output voltage lowers distortion.?
I¡¯ll add more in the morning when I¡¯m more awake.?
Jeremy?
On Sat, Dec 14, 2019 at 10:31 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
What's your secret Jeremy?? I have a couple of 200CDs but they are nothing to write home about regarding distortion.
Bob K6DX
On Saturday, December 14, 2019, 10:19:52 PM PST, Jeremy Nichols < jn6wfo@...> wrote:
My650A did fairly well distortion-wise but my favorite is the 200CD. With a few tricks and a little tweaking I was able to get it down to 0.04%, well below spec.
Jeremy
On Sat, Dec 14, 2019 at 9:43 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
I know this doesn't help but I did want to say that, in all my years of working with HP gear, this circuit is about the worst design.? I have repaired my 651A a couple of times and have never been able to get it to meet its distortion spec.? Mine works okay but I got tired of messing with it and it's no longer in line for use.? My main repair seemed to center about that FET in the middle of the diagram.? I tried a few different types without much success.? I ddi finally get it to oscillate on all ranges.? The distortion runs a bit over 0.5% worst case and the frequency calibration isn't as good as it could be, but it remains a useful instrument.
Perhaps you'd like to play with it.? The main thing I like is the nice attenuator.? Back in the day, I had a 650A that was a marvelous piece of gear.? Too bad this one didn't match that.
Bob
On Saturday, December 14, 2019, 08:35:49 PM PST, Don Bitters via Groups.Io <donbitters= [email protected]> wrote:
Almost certainly 50Hz AM modulation - 20msec per cycle.? Does touching the 645 chassis change the amplitude of the modulation, if so check the chassis ground at the power cord input, you may have an open ground pin.? If not check the power supplies for 50/100 Hz modulation, percentage of voltage of the supply, the worst looking supply is probably the culprit. Don Bitters
-- Jeremy Nichols
6.
-- Jeremy Nichols
6.
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Re: OT? Comb mixer, drive level?
Is this for the input receiver section, or the output source section? It seems you're describing an input signal downconverter/sampler. The comb is likely made from the VHF drive power by an SRD, so +20 to 30 dBm is in the right ballpark for level. The output from the SRD then drives the actual input signal mixer to convert down to the IF. The SRD's conversion loss, and the fact that the output power is spread among many harmonics, should still leave enough mixer LO power - perhaps up to a few dBm - at any particular desired harmonic, once it's optimized for it. The instrument's brain should know the correct drive frequency to apply, the harmonic, and the desired IF. It may also control the level into the PA, and the SRD's DC bias, depending on the frequency, so it can get rather complicated. If you have adjusted a tuning network at the PA output, you may have upset things - that may be the matching network for the SRD itself, if it's not built into the comb mixer module. Each SRD is fairly unique in response, so the matching network is adjusted to maximize the efficiency and flatness of the resulting comb output, not necessarily the PA's output. Once you figure out what's supposed to be going on in there (hopefully finding the manual), you may want to step back and see what the adjustments are for.
Ed
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Re: OT? Comb mixer, drive level?
Have a look at the HP microvawe accessories catalogs around 1970 -1980 : a chapter is devoted to their comb generators. On Sunday, December 15, 2019, 7:07:20 PM GMT+1, Staffan <testjarfalla63@...> wrote:
Hello,
Thanks. Any idea where I can find that manual? Checked ko4bb and Baman, but didn't seem to be there.?
Any idea what power level was used?
Regards,
? Staffan
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Re: Help to repair my HP654A Test Oscillator
Jeremy, I couldn't find anything on 200CD in EL34 website.? But the other one yielded essentially the same info as you gave on level setting.
I am resisting the temptation to get into these oscillators.? I don't have bench space and too many things going on.? But soon.
Bob
On Sunday, December 15, 2019, 01:34:00 PM PST, Jeremy Nichols <jn6wfo@...> wrote:
Matching tubes: I didn¡¯t want to repeat myself. For my 200CD, I found a matched pair of 8425A¡¯s (the industrial version of 6AU6A) for V1 and V3. (Please don¡¯t tell HP they¡¯re Tektronix tubes!) For V2 and V4 (6CW5) I found a nice pair of Made-in-Holland Amperex tubes in my spares box.?
I agree the prices on eBay are steep and that seems to be so for much older HP equipment. Clearly, sellers don¡¯t understand that the market is limited for this stuff. The ¡°sold¡± listings on eBay range from $15.50 to $150. Plus shipping, of course. Flea markets and estate sale prices are much more attractive.?
There is some good 200CD information in <> search for ¡°HP 200CD oscillator repair.¡±?
Another good link is <>. Under ¡°General Vintage Technology/Success Stories¡± search for ¡°Hewlett Packard 200CD Wide Range Oscillator.¡±
Jeremy? N6WFO
On Sun, Dec 15, 2019 at 10:35 AM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
I will have to check my serial numbers.? Your most recent message didn't mention matching tubes.
Anyway, this is interesting.? The easiest mods would be to lower the amplitude and improve the lamp sockets.? I will do those first and see what I get.? If results are promising I can get rid of the function generator.? Matching tubes can only work if both units use the same type, or I can find a source of them.? Buying tubes in hopes of finding a good match and then seeing if that helps seems a waste of effort and money.
I have two of these, one is rack mount and I don't want to preserve that one.? So I will concentrate on improving the cabinet mounted unit.
Perusing ebay shows that you can't buy a working unit for less than about $100.? I am amazed that their perceived value is that high.? Once this is done I may put one or both on ebay depending on distortion.? Of course I can brute force lower distortion with a filter but that makes for another project.
Bob K6DDX
On Sunday, December 15, 2019, 10:02:20 AM PST, Jeremy Nichols < jn6wfo@...> wrote:
*** Distortion of the HP-200CD ***
I used my HP-330B Distortion Analyzer to check the 200CD. The 330B is a vacuum tube unit; 0.04% is definitely pushing its limits; it probably would be more fair to claim my 200CD's distortion is "less than 0.1%."
*** Additional information on the HP-200CD Audio Oscillator. ***
1. The later versions using miniature tubes have lower distortion than the earlier versions with octal tubes. The split appears to have taken place at serial prefix 103, which also introduced Dynamic Balance Adjust pot R50 and Hum Balance pot R51.
2. The 200CD was listed in HP catalogs beginning in late 1951 ($150) and was last in the 1985 catalog (un-priced but I have been told it sold for $1250). This 34-year production run is probably a record for HP. The 200CD was HP's second-to-last vacuum tube instrument. One of this nice things about this long run is that there are a zillion of them still floating around for those of us who like to play with the descendants of HP's very first product.
3. The internal pot that sets the maximum output is R11 (1000 Ohms), which is normally set for a 24 Volt no-load output at 1000 Hertz (12 Volts into a 600 Ohm load). If the output is reduced below 10 Volts (loaded) the distortion is reduced; below 7.5 Volts is even better. Clearly, if your application requires higher voltage, you have to live with more distortion.
4. The manual sold by Artek (CD or download) includes in the second volume a group of HP "Service Notes" that are especially valuable for those owning early models using octal tubes. 5. The last revision appears to carry serials prefixed "960-" or "0960A." These final versions use solid-state rectifier diodes and have a standard IEC plug-in power cord.
It's interesting that the 200CD does not have a regulated power supply, only a pi-network filter.
The solid-state rectifier does not make much, if any improvement in distortion. (My "best" 200CD carries serial prefix "333-.")
6. Some excellent information, copied from the old Ampex mailing list, is posted in . This includes detailed information on the 7.5 Volt modification (which I did not do to my 200CD). 7. In the last versions, the sockets for resistor lamps RT1 and RT2 are mounted on a small pc board (with other components). Ensuring good contact between the sockets and the traces can be challenging due to the riveted construction.
Jeremy
On Sat, Dec 14, 2019 at 11:38 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
Okay Jeremy I appreciate it.? I have two 200CDs and am sure I can glean a matched pair of tubes from the four.? In any case I am interested in taking this far enough to at least approach the amount of distortion you have.? How did you measure it, and under what settings and conditions?
I have a 331A but don't use it.? A VNA I have does go down into the audio, as well as the FFT in one of my scopes and I can measure distortion that way.? I never measured anything as low as 0.04% though.
Bob K6DDX
On Saturday, December 14, 2019, 11:29:55 PM PST, Jeremy Nichols < jn6wfo@...> wrote:
There are a number of tricks that have been published over the years. I¡¯ll send you copies tomorrow. In the?meantime,? ? balance the two pairs of tubes that make up the push-pull oscillator. The pairs of tubes don¡¯t have to be new/perfect but should be as close as possible in terms of gain.? ? make sure the two lamps in the oscillator feedback have clean bases, are making tight contact with clean sockets, and the sockets have good solder connections. Sockets that are mounted with rivets to a pc board are especially susceptible to poor contact.? ? use the internal gain control (tomorrow I can give you the R-number) to reduce the maximum output to 10 Volts, perhaps even less depending on your needs. Reducing the output voltage lowers distortion.?
I¡¯ll add more in the morning when I¡¯m more awake.?
Jeremy?
On Sat, Dec 14, 2019 at 10:31 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
What's your secret Jeremy?? I have a couple of 200CDs but they are nothing to write home about regarding distortion.
Bob K6DX
On Saturday, December 14, 2019, 10:19:52 PM PST, Jeremy Nichols < jn6wfo@...> wrote:
My650A did fairly well distortion-wise but my favorite is the 200CD. With a few tricks and a little tweaking I was able to get it down to 0.04%, well below spec.
Jeremy
On Sat, Dec 14, 2019 at 9:43 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
I know this doesn't help but I did want to say that, in all my years of working with HP gear, this circuit is about the worst design.? I have repaired my 651A a couple of times and have never been able to get it to meet its distortion spec.? Mine works okay but I got tired of messing with it and it's no longer in line for use.? My main repair seemed to center about that FET in the middle of the diagram.? I tried a few different types without much success.? I ddi finally get it to oscillate on all ranges.? The distortion runs a bit over 0.5% worst case and the frequency calibration isn't as good as it could be, but it remains a useful instrument.
Perhaps you'd like to play with it.? The main thing I like is the nice attenuator.? Back in the day, I had a 650A that was a marvelous piece of gear.? Too bad this one didn't match that.
Bob
On Saturday, December 14, 2019, 08:35:49 PM PST, Don Bitters via Groups.Io <donbitters= [email protected]> wrote:
Almost certainly 50Hz AM modulation - 20msec per cycle.? Does touching the 645 chassis change the amplitude of the modulation, if so check the chassis ground at the power cord input, you may have an open ground pin.? If not check the power supplies for 50/100 Hz modulation, percentage of voltage of the supply, the worst looking supply is probably the culprit. Don Bitters
-- Jeremy Nichols
6.
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Re: Help to repair my HP654A Test Oscillator
Matching tubes: I didn¡¯t want to repeat myself. For my 200CD, I found a matched pair of 8425A¡¯s (the industrial version of 6AU6A) for V1 and V3. (Please don¡¯t tell HP they¡¯re Tektronix tubes!) For V2 and V4 (6CW5) I found a nice pair of Made-in-Holland Amperex tubes in my spares box.?
I agree the prices on eBay are steep and that seems to be so for much older HP equipment. Clearly, sellers don¡¯t understand that the market is limited for this stuff. The ¡°sold¡± listings on eBay range from $15.50 to $150. Plus shipping, of course. Flea markets and estate sale prices are much more attractive.?
There is some good 200CD information in <> search for ¡°HP 200CD oscillator repair.¡±?
Another good link is <>. Under ¡°General Vintage Technology/Success Stories¡± search for ¡°Hewlett Packard 200CD Wide Range Oscillator.¡±
Jeremy? N6WFO
On Sun, Dec 15, 2019 at 10:35 AM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
I will have to check my serial numbers.? Your most recent message didn't mention matching tubes.
Anyway, this is interesting.? The easiest mods would be to lower the amplitude and improve the lamp sockets.? I will do those first and see what I get.? If results are promising I can get rid of the function generator.? Matching tubes can only work if both units use the same type, or I can find a source of them.? Buying tubes in hopes of finding a good match and then seeing if that helps seems a waste of effort and money.
I have two of these, one is rack mount and I don't want to preserve that one.? So I will concentrate on improving the cabinet mounted unit.
Perusing ebay shows that you can't buy a working unit for less than about $100.? I am amazed that their perceived value is that high.? Once this is done I may put one or both on ebay depending on distortion.? Of course I can brute force lower distortion with a filter but that makes for another project.
Bob K6DDX
On Sunday, December 15, 2019, 10:02:20 AM PST, Jeremy Nichols < jn6wfo@...> wrote:
*** Distortion of the HP-200CD ***
I used my HP-330B Distortion Analyzer to check the 200CD. The 330B is a vacuum tube unit; 0.04% is definitely pushing its limits; it probably would be more fair to claim my 200CD's distortion is "less than 0.1%."
*** Additional information on the HP-200CD Audio Oscillator. ***
1. The later versions using miniature tubes have lower distortion than the earlier versions with octal tubes. The split appears to have taken place at serial prefix 103, which also introduced Dynamic Balance Adjust pot R50 and Hum Balance pot R51.
2. The 200CD was listed in HP catalogs beginning in late 1951 ($150) and was last in the 1985 catalog (un-priced but I have been told it sold for $1250). This 34-year production run is probably a record for HP. The 200CD was HP's second-to-last vacuum tube instrument. One of this nice things about this long run is that there are a zillion of them still floating around for those of us who like to play with the descendants of HP's very first product.
3. The internal pot that sets the maximum output is R11 (1000 Ohms), which is normally set for a 24 Volt no-load output at 1000 Hertz (12 Volts into a 600 Ohm load). If the output is reduced below 10 Volts (loaded) the distortion is reduced; below 7.5 Volts is even better. Clearly, if your application requires higher voltage, you have to live with more distortion.
4. The manual sold by Artek (CD or download) includes in the second volume a group of HP "Service Notes" that are especially valuable for those owning early models using octal tubes. 5. The last revision appears to carry serials prefixed "960-" or "0960A." These final versions use solid-state rectifier diodes and have a standard IEC plug-in power cord.
It's interesting that the 200CD does not have a regulated power supply, only a pi-network filter.
The solid-state rectifier does not make much, if any improvement in distortion. (My "best" 200CD carries serial prefix "333-.")
6. Some excellent information, copied from the old Ampex mailing list, is posted in . This includes detailed information on the 7.5 Volt modification (which I did not do to my 200CD). 7. In the last versions, the sockets for resistor lamps RT1 and RT2 are mounted on a small pc board (with other components). Ensuring good contact between the sockets and the traces can be challenging due to the riveted construction.
Jeremy
On Sat, Dec 14, 2019 at 11:38 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
Okay Jeremy I appreciate it.? I have two 200CDs and am sure I can glean a matched pair of tubes from the four.? In any case I am interested in taking this far enough to at least approach the amount of distortion you have.? How did you measure it, and under what settings and conditions?
I have a 331A but don't use it.? A VNA I have does go down into the audio, as well as the FFT in one of my scopes and I can measure distortion that way.? I never measured anything as low as 0.04% though.
Bob K6DDX
On Saturday, December 14, 2019, 11:29:55 PM PST, Jeremy Nichols < jn6wfo@...> wrote:
There are a number of tricks that have been published over the years. I¡¯ll send you copies tomorrow. In the?meantime,? ? balance the two pairs of tubes that make up the push-pull oscillator. The pairs of tubes don¡¯t have to be new/perfect but should be as close as possible in terms of gain.? ? make sure the two lamps in the oscillator feedback have clean bases, are making tight contact with clean sockets, and the sockets have good solder connections. Sockets that are mounted with rivets to a pc board are especially susceptible to poor contact.? ? use the internal gain control (tomorrow I can give you the R-number) to reduce the maximum output to 10 Volts, perhaps even less depending on your needs. Reducing the output voltage lowers distortion.?
I¡¯ll add more in the morning when I¡¯m more awake.?
Jeremy?
On Sat, Dec 14, 2019 at 10:31 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
What's your secret Jeremy?? I have a couple of 200CDs but they are nothing to write home about regarding distortion.
Bob K6DX
On Saturday, December 14, 2019, 10:19:52 PM PST, Jeremy Nichols < jn6wfo@...> wrote:
My650A did fairly well distortion-wise but my favorite is the 200CD. With a few tricks and a little tweaking I was able to get it down to 0.04%, well below spec.
Jeremy
On Sat, Dec 14, 2019 at 9:43 PM Bob Albert via Groups.Io <bob91343= [email protected]> wrote:
I know this doesn't help but I did want to say that, in all my years of working with HP gear, this circuit is about the worst design.? I have repaired my 651A a couple of times and have never been able to get it to meet its distortion spec.? Mine works okay but I got tired of messing with it and it's no longer in line for use.? My main repair seemed to center about that FET in the middle of the diagram.? I tried a few different types without much success.? I ddi finally get it to oscillate on all ranges.? The distortion runs a bit over 0.5% worst case and the frequency calibration isn't as good as it could be, but it remains a useful instrument.
Perhaps you'd like to play with it.? The main thing I like is the nice attenuator.? Back in the day, I had a 650A that was a marvelous piece of gear.? Too bad this one didn't match that.
Bob
On Saturday, December 14, 2019, 08:35:49 PM PST, Don Bitters via Groups.Io <donbitters= [email protected]> wrote:
Almost certainly 50Hz AM modulation - 20msec per cycle.? Does touching the 645 chassis change the amplitude of the modulation, if so check the chassis ground at the power cord input, you may have an open ground pin.? If not check the power supplies for 50/100 Hz modulation, percentage of voltage of the supply, the worst looking supply is probably the culprit. Don Bitters
-- Jeremy Nichols
6.
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Re: seeking schematic and any experienced advice FOLLOW-UP MESSAGE with correct model number
Hi,
The Vega 450 datasheet and manual are available online and the supply should run OK without any load. Checking the supply out of the scope is best approach. I do have a spare Vega 450 with 2 low voltage and 2 12V output modules but would have to check the currents.
Robert G8RPI.
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Re: seeking schematic and any experienced advice FOLLOW-UP MESSAGE with correct model number
From personal experience with that flavour of SMPS in other products.??
It's more likely that the PFC front end has "blown up!"
They are fairly easy to remove the PCB's, upon which you'll easily see
the tell-tale marks of disaster.
I had one though, where one of the regulator cards had gone short-cct at
it's HVDC input, destroying itself, and taking the input card too (as
well as blowing one of the interconnect pins, like a fuse-wire!)
Like many similar things, there is a lot of current going round in
circles in those PSU's, and any compromise in cooling seems to push them
over the edge, even if the load is well within spec'.
TDK Lambda in the UK are reachable, and have a repair service, should
you need.? I don't know if they have similar facilities elsewhere on the
planet, other than perhaps the far east, where a lot of the modules are
actually manufactured.
73.
Dave B.
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Jeremy Nichols