Re: AFG/RFG controls R4C (W1ES)
On 2025-01-08 17:18, Steve Wedge, W1ES/4 via groups.io wrote: Funny thing is, lately, my TR7 is the rig that most benefits from
lowering the RF gain a tad. Lots of popping on fast AVC, otherwise.
The A's and B's areen't as bad. The C is in between... *** My latest boat anchor project REALLY wants the RF gain set down. It's a Signal/One CX7A. Signal One messed up the injection to the product detector, and if you have the RF gain all the way up, it distorts. Voices sound harsh. There's a fix - you change one resistor. Waiting for me to get a round tuit. - Jerry, KF6VB
|
Re: 6HS6 Price and Availability
I meant to say that my memory the 6AU6 has a reputation for being mechanically noisy. It is also a sharp cut-off pentode, not good for use with AVC circuits. However, a sharp cutoff tube can be used with some tailoring of bias, as in the 51J series which uses the 6AK5.
toggle quoted message
Show quoted text
On 1/8/2025 8:22 PM, Richard Knoppow via groups.io wrote: ?? The 6BA6 is fairly common as an RF amp, see for instance the SP-600
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Re: 6HS6 Price and Availability
The 6BA6 is fairly common as an RF amp, see for instance the SP-600 and other receivers. It has good dynamic range which may be more important than noise level. It is essentially a variable mu version of the 6AU6. By memory the 6HS6 has a higher Gm than the 6BA6, which would make it quieter.
A very long time ago I did some experimenting with RF amps in an old Super-Pro which was my test bed. Tried many exotic tubes and different circuits including a cascode amp. Wound up using the 6BA6 due its ability to handle a wide dynamic range.
When I bought the receiver the entire RF section had been rebuilt by someone using dual triodes. It sort of worked but I decided to try other things.
toggle quoted message
Show quoted text
On 1/8/2025 5:19 PM, Paul Christensen via groups.io wrote: Drake¡¯s R4 series RF amp evolution is interesting.? It began with a 12BZ6 in the original R4/R4A, changed to a 6HS6 in the R4B, ending with a 6BA6 in the R4C.? The latter is commonly found in many IF circuits, including Drake but not too often used as the 1^st RF amp.? Can anyone guess as to Drake¡¯s impetus for the change? ?Seems like all three tube types were available at the beginning of R4 production.
Paul, W9AC
--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
|
Re: 6HS6 Price and Availability
Paul raises a very interesting question, What prompted the evolution of device selection for RF amp and 1st mixer in Drake's receivers?
?
12BZ6/6AU6 -> 12BZ6/6HS6 -> 6HS6/6HS6 -> 6BA6/6EJ7? ? if I have the sequence correct.
?
ChatGPT tells me they went with 40673 MOSFETs at some point later on, but I doubt any of those ended up in the R-4x line. I'll be corrected if so.
?
I'll throw out a hypothesis:
?
The initial R-4 design was likely based on what they were used to using in earlier product lines. Getting the new receiver out the door quickly and into the market to support the company was probably very important.
?
I remember in the 70s hams experimenting with various tubes to "soup up" the front ends of their radios. These new types had higher transconductance and lower noise than what the factory supplied -- 6BZ6/6CB6/6GM6/6HS6, etc., and were all sharp-cutoff pentodes. No doubt the engineers at Drake took notice of this and did their own research and experimentation, developing lower-noise, more sensitive receiver front-ends for weak signals. All well and good, until...
?
Customers started complaining about IMD and front-end overload in crowded contest conditions. Probably around this time test equipment of high enough quality to measure these effects also became available. Engineers were sent back to the drawing board to see what could be done to fix that issue. Reaching back into the dusty pages of some old data books, someone remembered the old, reliable 6BA6, which had been used in TV receivers for years. It's a remote-cutoff pentode with lower transconductance, but better dynamic range capability than the high sensitivity tubes. The resulting design was a good compromise between sensitivity and IMD. I haven't heard of Drake front-ends becoming unstable, but almost certainly the 6BA6 was a more stable tube than the ones with higher transconductance.
?
I wasn't present at Drake, I have no first-hand or historical knowledge, nor a deep technical understanding of receiver design, and all of this could be complete rubbish. But I toss it out to generate a discussion.?
?
Dave
|
I had left the rig powered on overnight after working a number of guys.? Came back the next morning and the rig was showing no life.? Fuse was popped.
With the rig on the bench, I could turn on the power and after maybe 20-30 seconds, I could see an arc starting on the tune cap. On close examination of the tune cap, 4 of the plates in one section had arced enough to have slightly melted away a bit of the plates on the fixed half.
Repaired the damage and checked the cap out with the HV leakage tester - looked good to about 1500V or so. Put it all back together and almost put it back on the shack shelf when it occurred to me.? With the rig sitting at idle, there should be NO voltage across the tune cap.? That assumes the coupling cap was working properly in it's DC-block role.? I replaced the 2700pf/2KV with a 4700pf 3KV ceramic I had in the junk box and then put it back on the shack shelf for check out.
Tested the old coupling cap and the leakage even at 1KV was only slightly higher than the new Vishay ceramic part I had put in as the replacement.? Even warmed it up with the heat gun - no change.? This is pretty weird as I almost never see ceramics leak but maybe they do.
The rig is working fine now although power is about 1/3 to 1/2 what I would expect.? The unloaded HV was OK when it was on the bench and I'm thinking there may be another problem.? I can't imagine that a leaking coupling cap, arcing through the tune cap, would damage the finals though.
Wanted to toss that scenario out and see if anyone on the reflector may have run into a similar case in the past.
HNY!
--
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
|
Re: 6HS6 Price and Availability
Thanks for this no-guesswork essay, Steve. ?Maybe when time avails, quantitative testing will be done and published.
?
73, Michael, N4KZO
|
Re: 6HS6 Price and Availability
Roger that, John.
?
73, Michael, N4KZO
|
Re: 6HS6 Price and Availability
Thank you, Gary: a little good engineering ¡ª love it.
?
73, Michael, N4KZO
|
Re: 6HS6 Price and Availability
Good work, Dave. ?Thank you for your efforts in experimental tests to resolve this drama: learning, learning, we never stop learning
?
73, Michael, N4KZO
|
Re: 6HS6 Price and Availability
Thank you, Kim. ?Doing a little looking around, I¡¯ve found bunches and grunions of NOS 6AH6 tubes: say $3 - $4 EACH. ?You answer which immediately comes to my mind, as to why the 6HS6 was chosen by Drake engineering. ?With the present atmospheric noise level, the 6AH6 should work fine, if present; when it gets quiet again, I can check use of the 6AH6 as an experiment as I think I have all 6HS6¡¯s. ?But, as Peter has elucidated, we don¡¯t need to concerned; I¡¯m working on getting a B-line going and haven¡¯t assessed a need, but I¡¯m sleeping easy: a good lesson.
?
73, ?Michael, N4KZO
|
Re: 6HS6 Price and Availability
Good job, Peter. ?Good lesson for me. Thank you.
zzzzzzzzzzzzzzzzzzz
73, Michael, N4KZO
|
Re: Using the PLJ-6LED digital display with the R4C
P.S. ? I would first start with only Q1 to rule out any effect cable capacitance is having on the RF voltage level between INJ and the digital display.? The display spec sheet indicates that it should function with way less than you measured at INJ. If necessary, then add Q2. ? Paul, W9AC ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Paul Christensen via groups.io
Sent: Wednesday, January 8, 2025 8:13 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] Using the PLJ-6LED digital display with the R4C? Floyd, ? WB6OGD pointed to a good go-to reference from Elecraft.? Have a look at the schematic on p. 27 and refer to Q1 and Q2.? Q1 (J310) has a gain less than unity as a source follower.? However, it¡¯s then amplified by Q2 (MPSH10) in a collector-feedback circuit formed by R3/R6.? Install at the INJ point.? Use capacitive coupling from the Q2 collector to your new digital display. ?
? Paul, W9AC ? ? Possibly consider a J310 JFET as a common-source amp placed right at the source of the INJ jack. Resistors chosen for a gain of A = 2 (6 dB) to get over the minimum RF sample voltage requirement. ? ? The JFET unloads the INJ line to the Hi-Z gate and that isolates the INJ source from cable capacitance to the freq. counter.? With adequate PS decoupling, probably a half-dozen parts are needed, mounted either on a 5-6 lug terminal strip or Vector board.? ? The common I.F. output buffers often seen are common-drain source-followers with a gain of less than 1.0.? That won¡¯t work in this instance to solve the problem.? ?
Paul, W9AC ? That sounds like the solution, Paul, but I'm afraid I'm not capable of doing that probably simple design.? Can you point me to an existing example, or, do a simple design ?? Not sure why I seem to be the only one who ever had a problem with the available INJ signal level, but maybe others haven't actually tested their configuration on 10 and 15 meters with the T4X connected to the INJ cable.? Without that connection, the signal level is adequate to provide a stable readout in my case on the highest bands. ? 73, Floyd - K8AC??
|
Re: 6HS6 Price and Availability
Drake¡¯s R4 series RF amp evolution is interesting.? It began with a 12BZ6 in the original R4/R4A, changed to a 6HS6 in the R4B, ending with a 6BA6 in the R4C.? The latter is commonly found in many IF circuits, including Drake but not too often used as the 1st RF amp.? Can anyone guess as to Drake¡¯s impetus for the change? ?Seems like all three tube types were available at the beginning of R4 production.? ? Paul, W9AC
|
Re: AFG/RFG controls R4C (W1ES)
Funny thing is, lately, my TR7 is the rig that most benefits from lowering the RF gain a tad. Lots of popping on fast AVC, otherwise. The A's and B's areen't as bad. The C is in between...
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with Proton Mail secure email.
toggle quoted message
Show quoted text
On Wednesday, January 8th, 2025 at 7:48 PM, Jim Shorney via groups.io <jimNU0C@...> wrote: I guess you probably don't need to lower your noise floor for any reason. You must have DSP ears. I bet you can copy RTTY in your head too.
On Wed, 08 Jan 2025 14:19:37 -0800
"N3 EG via groups.io" n3eg@... wrote:
The RF Gain control has always been the most useless thing to put on a radio.
--
73
-Jim
NU0C
|
Re: If you're going to be sloppy....
Oops.? I forgot about the FS-4 and I only took a quick peek -- didn't notice the shipping.? Yeah, free shipping at that price qualifies as a bargain!? If I was in the market, I probably would have paid more attention...
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Wednesday, January 8th, 2025 at 7:55 PM, Gary WB6OGD via groups.io <winbladgary@...> wrote:
Come off?
That is the rare FS-4 sticker overlay everyone is looking for!
Implies there are no extra crystals inside but it has been used with the FS-4.
$220 for a nice looking, working T-4XC is a good deal with free shipping..? it sold quickly I guess.
73,
Gary
WB6OGD
|
Re: 6HS6 Price and Availability
No, James, nobody "jacked up" the price. As I previously mentioned, the price for this tube has been high for at least 30 years and probably longer.? There's no cabal of n'e'e'r-do-wells conspiring to deprive poor Drake aficionados of an extra $10 and nobody is buying real estate in KP2 with their proceeds.? The 6HS6's price is market-driven and a part of that is due to some tube audio companies using this tube in their lineup (Fisher being one).? There are more tube audio folks than tube radio folks, so we are splitting demand.
Drake initially was using the 6AU6 for both the first Mixer and the Premixer.in both the R-4 and the first T-4's.? They fairly quickly changed over to the 6HS6.? Though the actual decision-making is lost to the sands of time,it has been noted by others that the 6HS6 has better overall performance over the 6AU6,? The 6AH6 has nearly the same performance as the 6AH6 but, again, it's unknown why Drake chose one over the other.? The price at the time was likely a factor but not the only factor, as if price was the only factor, they would have stuck with the 6AU6 as it was available from nearly every vendor in massive quantities.? The 6HS6 was not as common even when they were current technology.
Here's the thing: most owners now use these rigs for relatively casual use.? They still hold their own (My opinion of my B Line is that it's a better rig than my Collins S Line, and there are reasons for that that I won't go into here).? These were used in contest stations up to the early 70's, when the C Line went into production and "brick-wall" filtering became a "must-have".? Under those conditions, the performance of the 6HS6 could reveal itself in the middle of a pileup.? I haven't made actual comparisons or tests.? Only subjective comparisons asnd my experience in the late 80s through around 1990, when I used a C Line for DXing and contesting as my only rig.
Today, when my 6HS6's are gone, I will gladly use 6AH6's in their place.? I have a small stock of 6AH6's (as well as 6HS6's, which I am not keen on selling even for $40). I have done limited testing on my R-4B with the 6AH6 subbed into both V2 and V8.? Steady-state signals reveal the same performance with either tube.? That isn't to say that IMD, etc., will also be the same but anyone interested can do the swap, hook up the equipment and publish their findings.
We should be happy that we only have that as the only uncommon tube in the linup (but don't get me started on 12BZ6 and some other early stuff).? Heathkit owners have to deal with Compactrons and some other strance stuff, so we are good here.
As always, YMMV.
73,
Steve Wedge, W1ES
Time flies like an arrow.? Fruit flies like a banana.
Sent with secure email.
On Wednesday, January 8th, 2025 at 5:12 PM, James Barrie via groups.io <barrie43@...> wrote:
I have used a 6AH6 in my R-4A for a year now with no issues. Maybe there was something magical about the 6HS6 when Drake decided to use it. My guess it was the cheapest tube that would work.
And I also suspect that a couple of tube vendors cornered a bunch of 6HS6s and jacked the tube's prices up blaming the audio people for the "scarcity".
It is pretty easy to make a solid state mixer. Unlike amplifiers, that need just a certain amount of amplification, extra AVC inputs, etc., mixers are
basically non-linear choppers. They just need enough gain to chop and enough voltage tolerance for the circuit they are in.
My very first experiment was a J-310 FET(the only FET I had) plugged into the R-4A Pre-mixer socket. I only had to disconnect the +150V plate supply resistor and hook it to about 18VDC(?). Worked fine though hooking it to the T-4X and selecting XMTR control might have blown it.
I researched more (stole designs and modded) and now have a plug in tube replacement. Works great.
Attached is what I think I am running now. I also attached a 6AU6 replacement from the Collins site.
Beats trying to buy expensive, possibly bad old tubes. YMMV.
My 6HS6 is now safe and part of my 401K IRA.. hi hi...
73,
Gary
WB6OGD
|
Re: Using the PLJ-6LED digital display with the R4C
Floyd, ? WB6OGD pointed to a good go-to reference from Elecraft.? Have a look at the schematic on p. 27 and refer to Q1 and Q2.? Q1 (J310) has a gain less than unity as a source follower.? However, it¡¯s then amplified by Q2 (MPSH10) in a collector-feedback circuit formed by R3/R6.? Install at the INJ point.? Use capacitive coupling from the Q2 collector to your new digital display. ?
? Paul, W9AC ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Floyd - K8AC via groups.io
Sent: Wednesday, January 8, 2025 3:38 PM
To: [email protected]
Subject: Re: [DRAKE-RADIO] Using the PLJ-6LED digital display with the R4C? Possibly consider a J310 JFET as a common-source amp placed right at the source of the INJ jack. Resistors chosen for a gain of A = 2 (6 dB) to get over the minimum RF sample voltage requirement. ? ? The JFET unloads the INJ line to the Hi-Z gate and that isolates the INJ source from cable capacitance to the freq. counter.? With adequate PS decoupling, probably a half-dozen parts are needed, mounted either on a 5-6 lug terminal strip or Vector board.? ? The common I.F. output buffers often seen are common-drain source-followers with a gain of less than 1.0.? That won¡¯t work in this instance to solve the problem.? ?
Paul, W9AC ? That sounds like the solution, Paul, but I'm afraid I'm not capable of doing that probably simple design.? Can you point me to an existing example, or, do a simple design ?? Not sure why I seem to be the only one who ever had a problem with the available INJ signal level, but maybe others haven't actually tested their configuration on 10 and 15 meters with the T4X connected to the INJ cable.? Without that connection, the signal level is adequate to provide a stable readout in my case on the highest bands. ? 73, Floyd - K8AC??
|
Ah the Analog Guru Jim Williams. I will always be in awe of the insight and knowledge that he had. On Tue, Jan 7, 2025 at 8:36?AM John E. Beck via groups.io <wb0rxl@...> wrote:
I would be happy to share it. It's always a work in progress, but let me clean it up a bit.
John
WB0RXL
|
Re: If you're going to be sloppy....
Come off?
That is the rare FS-4 sticker overlay everyone is looking for!
Implies there are no extra crystals inside but it has been used with the FS-4.
$220 for a nice looking, working T-4XC is a good deal with free shipping..? it sold quickly I guess.
73,
Gary
WB6OGD
|
Re: AFG/RFG controls R4C (W1ES)
I guess you probably don't need to lower your noise floor for any reason. You must have DSP ears. I bet you can copy RTTY in your head too. On Wed, 08 Jan 2025 14:19:37 -0800 "N3 EG via groups.io" <n3eg@...> wrote: The RF Gain control has always been the most useless thing to put on a radio. -- 73 -Jim NU0C
|
Paul Christensen
Gary WB6OGD
Jim Shorney