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Re: Another TR7 Journey begins
I don't think it really matters a whole lot. the TR7 wattmeter is not what I would call a precision instrument. Germanium was likely chosen for low forward voltage drop. A pair of decent Schottky diodes should work fine.
73 -Jim NU0C On Mon, 25 Mar 2024 17:28:39 -0700 "Bill NZ0T" <nz0tham@...> wrote: Thanks again Jim, |
Re: XTAL help is needed
Thank you to those who suggested AF4K Crystals.? I responded to an email from Nick earlier today regarding his need for a 10.0874 MHz crystal.? I let him know I can supply an inexpensive 10.080 MHz from stock in an HC-49 holder and this might be able to be pulled up in frequency to meet the target or at least get close. 73?? Steve? WD8DAS sbjohnston@...??
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Radio is your best entertainment value.??
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Re: Another TR7 Journey begins
Thanks again Jim,
I wonder if one or both of the AA119 diodes are bad in the wattmeter circuit.? They test OK in circuit with a multimeter but maybe they go leaky with more voltage applied.? Won't be easy to replace tho.? And I doubt they are easy to find tho I think the 1N60 is pretty close.? They are germanium diodes. I'll try checking voltages in the circuit in the morning. 73, Bill NZ0T |
Re: XTAL help is needed
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The March/April 2024 issue of Electric Radio has an article about using a ProgRock "programmable crystal" in the restoration of a Heathit HX-1681.? Interesting information on how to program it and integrate it into the circuit.
-- Art Delibert, KB3FJO
From: [email protected] <[email protected]> on behalf of Gary WB6OGD <winbladgary@...>
Sent: Monday, March 25, 2024 5:16 PM To: [email protected] <[email protected]> Subject: Re: [DRAKE-RADIO] XTAL help is needed ?
Or replace a whole bank of crystals(59?) for $14, see the Files section for:
$14 Homebrew FS-4B Old fashioned crystals are obsolete!? hi hi... 73, Gary WB6OGD |
Re: Various Finds
Dang Gary I might be interested in the R7 as a challenge if Steve is not. If available please email me off list echapm4@...? Thanks,? Eric? K8cca? On Mon, Mar 25, 2024, 3:37?PM Gary Follett <xntrick1948@...> wrote: Steve: |
Re: 1-A on eBay
On 2024-03-25 14:25, John K5MO wrote:
On Mon, Mar 25, 2024 at 12:11 PM, Jim Shorney wrote: I just sold three vacuum tubes The three sold quickly enough to pay for half the cost of a new*** Many moons ago, I got three TV7D/U tube testers at the ham swap for $20 each. The price those things get on Ebay now.... is eye-watering. I think it's driven by audiophiles. - Jerry, KF6VB |
Re: 1-A on eBay
On 2024-03-25 13:24, Ralph Mowery via groups.io wrote:
It is easy to start off asking for a high price and lowering the*** I generally start walking way when the seller says "On Ebay these go for...." - Jerry, KF6VB |
Re: 1-A on eBay
John...nice going.? May we ask what the tubes were?? I fear I have a few "finds" lying dormant and lost in my tube stash too. 73 Peter VE7PS On Mon, Mar 25, 2024 at 2:25?PM John K5MO <johnk5mo@...> wrote: On Mon, Mar 25, 2024 at 12:11 PM, Jim Shorney wrote: |
Re: 1-A on eBay
On Mon, Mar 25, 2024 at 12:11 PM, Jim Shorney wrote:
An old salesman once said "don't charge a fair price, charge what the market will bear". If someone wants to spend that kind of money I just sold three vacuum tubes (old Western Electric) that I had found in one of the boxes of random pulls and NOS that I bought? 20+ yrs ago and never opened. They'd been lying on the garage floor since last November when I ran across them and I thought I should toss them on the 'Bay before I forgot about them for another 3 months. ? The three sold quickly enough to pay for half the cost of a new FTDX101D I now have on order.? :-) |
Re: Another TR7 Journey begins
Great! I've come to the point that 10-turn pots are a necessary upgrade. Those little trimpots can go off if you look at them wrong. They may have been primo parts in the day but time marches on.
Proper ALC depends on proper operation of the wattmeter circuit. Get the wattmeter working right. It's pretty much the same circuit as a W4. You can disconnect the FWD WM and REFL WM inputs from the ALC board if you want to isolate it, just watch your drive level. 73 -Jim NU0C On Mon, 25 Mar 2024 13:56:06 -0700 "Bill NZ0T" <nz0tham@...> wrote: Progress!? I went all the way back to the 10V setting which had moved to 9.1V for some reason - I can see why the 10 turn pots are a popular mod.? Got the oscillators? and VCXO within spec even the? 8.05 (just barely) without any cap padding. |
Re: Another TR7 Journey begins
Progress!? I went all the way back to the 10V setting which had moved to 9.1V for some reason - I can see why the 10 turn pots are a popular mod.? Got the oscillators? and VCXO within spec even the? 8.05 (just barely) without any cap padding.
So now I'm back to the transmitter alignment issues. I can get through the wattmeter null adjustment but the ALC adjustment is still wonky and, possibly because of that, the wattmeter is not working nor will it adjust. Will see what I can do tomorrow. 73, Bill NZ0T ? |
Re: 1-A on eBay
On Mon, 25 Mar 2024 20:17:47 +0000 (UTC)
"Paul Ellis via groups.io" <paulz67@...> wrote: Disclaimer: Your reality may vary.You kill me, man! I'm not sure I want to know about your reality.... :D I forgot to mention the nice R-390/A with original meters that I bought from Evan (NOT the Evan in this group) for $150. -- 73 -Jim NU0C |
Re: grounded grids vs stock Drake
W8JI did a good analysis of this idea:
Scroll down to 'A Common "Bad Grid Idea" Super Cathode Drive'. One take-away is that at some frequency in the HF spectrum that grid circuit is parallel resonant. That just seems like a bad idea. Of course this is not the only point in his analysis. 73 -Jim NU0C On Mon, 25 Mar 2024 20:21:46 +0000 "Clyde K2UE" <clydewashburn1@...> wrote: The mechanism of feedback is the capacitive divider formed by the plate -- 73 -Jim NU0C |
Re: grounded grids vs stock Drake
My homebrew single 3-500Z amp from the 1970s used directly-grounded grids. I see nothing wrong with Drake having added some negative feedback, but it wasn't consistent with frequency due the three 200pF capacitors per tube. Possibly this somewhat flattened out the drive requirement from 80 - 10 meters. (A supposition only)
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My amp used a 10-volt 50-watt zener diode grounded to the chassis for bias on SSB (likely a bit higher than optimum for linearity) with 2800 volts key down on the plate. During RX or on CW I switched in a 30-volt zener which was biased modestly beyond cutoff. For this project I purchased the 3-500Z from Drake for $35.00. Those were the days! Rob, NC0B -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Jim Shorney Sent: Monday, March 25, 2024 2:14 PM To: [email protected] Subject: Re: [DRAKE-RADIO] grounded grids vs stock Drake It seems worth noting that in recent years amplifier manufacturers have returned to the idea of directly grounding the grids. 73 -Jim NU0C On Mon, 25 Mar 2024 19:37:22 +0000 "Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote: I've been considering doing this, after a long stretch of keeping the grids slightly above DC ground. I've also been considering changing the bias to the stack o'zeners. I have a Harbach power supply board but I'm not sure if that has the alternative biasing on it. Currently, the amp idles at about 200 mA, which just seems excessive to me. I can get about 1200W out before the grids get overdriven (I like to keep the combined Ig below 300mA). |
Re: 1-A on eBay
It is easy to start off asking for a high price and lowering the asking price.? At hamfests I have bought and sold things at a price I wanted or walked away or? kept the items if the price was not to my liking.? As the day goes on the prices often get less. Probably the most expensive thing on earth for size or weight is totally useless.?? An old used postage stamp last sold for 8.3 million dollars. I think that is the only remaining one in the world. ?British Guiana 1c Magenta Ralph ku4pt
On Monday, March 25, 2024 at 03:11:34 PM EDT, Jim Shorney <jimnu0c@...> wrote:
An old salesman once said "don't charge a fair price, charge what the market will bear". If someone wants to spend that kind of money on a 1-A, that's fine. If no one bites the price will be reduced. I have gotten most of my good deals locally and some are almost legendary. Minty one owner R7A for $450, gently used L4B offered to me for $450 by a local who knew that I like Drake, an estate purchase of a TR7 station that netted me an L7 for about $150 after I cleaned the rest up and re-sold it to another local. Picked up a lonely PS7 for $75 at a fest a couple years ago so now I have one for each of my TR7s. Another local who likes to deal in used radios offered me a nice NC300 for 40 bucks just because he wanted to get it gone. A list member sold me an R7 a few years back for $300 because no one else was interested. One of my TR7s also from a list member for $150 as a fixer-upper. I won't even mention my deal of the century on the pair of Alphas.... Ebay? What's that? :D 73 -Jim NU0C |
Re: grounded grids vs stock Drake
Clyde K2UE
The mechanism of feedback is the capacitive divider formed by the plate to grid capacitance and the grid to ground capacitance.? The average of the various 3-500Z data sheets suggest plate to grid is 4.4 pF and each tube has 600 pF of grid to ground capacitance, so it is a a roughly 136:1 voltage divider.? Taking the 2500V case, the RMS plate voltage at 600W per tube is 1440V, which causes 10.6V to be applied to the grid, in opposition to the cathode.? ?The driving power without feedback is 46W into 100 ohms, or 67.8V, so the feedback has increased that to 78.4 V, or 61.5 W (ignoring the grid current loading).? So so in the simple case 33% more power is required for the same output.? Note that max output is not reduced -- it just takes more power to get there.? But if you have a 100W driver you are not able to supply more drive, and conclude that grounding the grids "makes more power".? With a 150 or 200W driver you crank up the power, get the same output as before, but reduced distortion due to the feedback. You can imagine the linearity enhancing effect by noting that the grid current shoots up at the peak of the drive cycle and is very non-linear.? So when the grid current is reaching peak it is shunting the feedback, i.e there is less negative voltage on the grid opposing the drive, helping the tube reach the peak current needed to accurately reproduce the peak -- in other words, better linearity. The above calculations are obviously an approximation, ignoring that the reactance of grid-to-ground capacitance changes by 16:1 over the various ham bands, and the grid input impedance in in shunt with it.? But that is the mechanism in a nutshell.
______________________________________________________________ Clyde Washburn "It is better to light one candle than to curse the darkness" ------ Original Message ------
From "Paul Kraemer" <elespe@...>
Date 3/25/2024 3:23:29 PM
Subject [DRAKE-RADIO] grounded grids vs stock Drake Curious as to what should actually be expected regarding power gain going from the "floating" grids in L4B / L7 vs strapping the grids directly to ground.? I see 200 watt increase on one L7. Increases from 1kw to 1200w, same drive level and power supply. Is that believable?? Seems a bit high but that is what I am seeing on one amp.
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Paul K0UYA
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Re: 1-A on eBay
This. The market for cool vintage gear has certainly shifted, as experienced hams are moving on and/or dying off, as always... In the meantime, pricing on new/shiny/SDR flavored gear has gotten insanely cheap, relative to the capabilities and performance -- which has increased dramatically over the past ten years or so. Will there be a market for classic gear in the future? Of course--not unlike the classic car hobby.? A few months back I posted my 1A for sale here, and all I heard was crickets. I'm pretty much over selling anything on eBay, so it also was marketed on Facebook Marketplace and Craigslist. I ultimately did a cash + trade for a Ten-Tec setup (locally-ish, with another member on this group) as a result of the Marketplace ad. The Ten-Tec setup, while it exceeded my expectations, will be hamfest fodder in the months ahead. Disclaimer: Your reality may vary. Paul KA0JQF |
Re: grounded grids vs stock Drake
It seems worth noting that in recent years amplifier manufacturers have returned to the idea of directly grounding the grids.
73 -Jim NU0C On Mon, 25 Mar 2024 19:37:22 +0000 "Steve Wedge, W1ES/4 via groups.io" <w1es@...> wrote: I've been considering doing this, after a long stretch of keeping the grids slightly above DC ground. I've also been considering changing the bias to the stack o'zeners. I have a Harbach power supply board but I'm not sure if that has the alternative biasing on it. Currently, the amp idles at about 200 mA, which just seems excessive to me. I can get about 1200W out before the grids get overdriven (I like to keep the combined Ig below 300mA). |