KC4VWU
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« on: September 20, 2009, 05:33:54 PM » |
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I dug this out today after several months of debating over what tubes to use. I had initailly wanted a pair of 4-400's in the PA, but I had to get back to reality. I have quite a few 813's also, and this would definately give me a pretty good head start. I remembered that I had bought this several years ago to save it from "CB amplifier" conversion; someone obviously put a lot of effort in building it. It appears that it was set up for 20M when I got it since the the input coil is labeled as such. I don't know what happened to the coils mounted to the output jackplate, but I do have the remnants of the swinging link.
Any ideas? Strip it and use the basis on a Pi-net, or rebuild it as link coupled output? Does the latter actually need to have a swinging link, or can it be fixed; especially if I was going to use it as a monoband TX (75M)?
Phil
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W2PFY
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« Reply #1 on: September 20, 2009, 07:27:37 PM » |
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If you found yourself a bunch of BC-610 coils with the variable link inside, you could use it pretty much as it was designed. The coils with fixed coil will also work but you would need to put a variable cap in series with the ground side of the link to ground, for it to avoid over coupling the final on some bands. The coils with the fixed link that look like BC-610 coils are in reality the input coils for the BC-610 amplifier know as the AM-141.
What is that big resistor in there? It looks to be a very low value?
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KC4VWU
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« Reply #2 on: September 20, 2009, 08:47:16 PM » |
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It looks to be in series with the filament transformer primary along with the front panel mounted rheostat. The transformer is a Stancor P-2030. I haven't researched it yet, but maybe it isn't a 10v 10A unit; maybe a 12v and that is why the use of the monster resistor. It would have 10A flowing through it? Rheostat doesn't look that tough though.
Phil
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W2PFY
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« Reply #3 on: September 20, 2009, 09:01:36 PM » |
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The resistor thing could work in your favor by eliminating inrush currents to your filaments. Lots of old buzzard rigs used them. Perhaps they were cheaper than variacs or were around before variacs? It a good basis for a nice HF amplifier  |
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KM1H
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« Reply #4 on: September 20, 2009, 09:14:01 PM » |
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Having the input network right next to the tubes is real sloppy design. At least have a shield between them or better still put it underneath.
Also lower the 813 sockets down so that the visible grid leads are below the chassis.
A pi network output and parallel tubes might be a better choice depending what you want to use it for.
Carl
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N3DRB The Derb
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« Reply #5 on: September 21, 2009, 12:25:44 AM » |
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I think the nameplate on the transformer reads P-3020 not P-2030.
stancor P-3020 is 11.0 ct @10 amps.
I wish I could find a place that has those old buzzard style nameplates concerning radio that you could buy new.
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KC4VWU
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« Reply #6 on: September 21, 2009, 01:14:08 AM » |
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You're right Derb, I'm going to have to get my eyes checked again! It did say P-3020 -- maybe a little dyslexia too!
I'm just going to settle on 813's and start sketching out a layout tomorrow. I'll worry about the modulator after I get the Tx. up and running. Probably going to drive it with an ARC-5.
I just ran across an article in an old ARC issue where a guy made them like etching PC boards. I can scan it and send you a copy if you'd like.
Phil
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KC4VWU
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« Reply #7 on: September 21, 2009, 03:21:48 AM » |
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Last part of that referring to the nameplates.
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N3DRB The Derb
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« Reply #8 on: September 21, 2009, 05:39:09 AM » |
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that would be kool, tnx.  Pair of 813's will strap big time, no need to apologize there. |
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KM1H
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« Reply #9 on: September 21, 2009, 10:18:21 AM » |
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Forgot to mention earlier that if you want the best stability with 813's use sockets that have the push and lock metal bases and ground them good. The GE tubes with the ground ring built in the envelope aid stability also.
Carl
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N3DRB The Derb
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« Reply #10 on: September 21, 2009, 12:32:08 PM » |
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means a rf ground - use some good copper STRAP to ground it, no little tiny wire. use the screw that mates the metal shell to the ceramic on both sides. |
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KC4VWU
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« Reply #11 on: September 21, 2009, 01:25:12 PM » |
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Tim, I sent the nameplate article. Pretty cool idea.
I'm going to start taking that deck apart today to get it to a workable level. I'll post my progress on it.
Phil
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W2PFY
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« Reply #12 on: September 21, 2009, 01:38:35 PM » |
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Tim, I sent the nameplate article. Pretty cool idea. Tim who? Tiny Tim |
The secrecy of my job prevents me from knowing what I am doing.
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W2PFY
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« Reply #13 on: September 23, 2009, 02:51:49 PM » |
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Tim who? Tiny Tim Grin Grin Thanks for no help guys I finally figured out that the Derb is a Tim. I always thought that was your first name Derb. My next project is designing an outhouse for the moon. Any suggestions? |
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The secrecy of my job prevents me from knowing what I am doing.
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KC4VWU
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« Reply #14 on: September 23, 2009, 08:54:49 PM » |
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Sorry O.M. I've been wearing blisters on my digits working a flat file on this front panel refurb. Figured out his name when I got his Email, but I guess we can call him Mr. Derb.
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VE3GZB
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« Reply #15 on: September 23, 2009, 10:29:17 PM » |
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Very nice rig! I'm jealous!  |
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N3DRB The Derb
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« Reply #16 on: September 23, 2009, 10:56:07 PM » |
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derb came about from N3DRB.
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KC4VWU
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« Reply #17 on: September 24, 2009, 12:41:46 AM » |
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Yeah, I kinda figured. Actually I'm pretty familiar with it another way. I worked for Chrysler dealerships for about 10 years as a line tech. The Chrysler "scan tool" is called a DRB. With only 2 DRB's in a shop of about 20 techs, you would hear throughout the day "Hey! Who's got the Derb!" About 80% of the work required the use of the DRB III. You could own one of those setups complete, if you had about $10K to part with. Not many mechanics I knew who were that fortunate.
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KC4VWU
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« Reply #18 on: September 25, 2009, 08:18:43 AM » |
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O.K. guys, I have this chassis stripped and I'm trying to figure out which way to go. This being my first big HB rig, should I go for the gusto with the 2 x 813 PA, or start with somthing simpler like triodes; 572B's or 811A's? Like I stated before, this will be a 75M single bander for now. No bandswitching to fuss with. I'm set with enough parts to go either way, just needing a little advice from others who have already been there.
Phil
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N2DTS
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« Reply #19 on: September 25, 2009, 08:36:40 AM » |
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I have built both.
I had a push pull 812A rig modulated by 811A's, with seperate power supplies.
Smooth working rig!
I used KW plug in coils and 30kv miniture vacuum variables for neutralizaton caps (out of an old 4-400 paging transmitter).
Very nice 300 watt rig. I sold that rig to somebody who paid to have it crated up and shipped to Washington state I think!
I also built the 2x813 rig. Another smooth working rig, and very robust, 600 watts carrier all day long.
You cant go wrong with 813's.
I guess it depends on what you have for modulators.
I always want as much audio power as carrier output power, that is 600/700 watts for the 813's.
If you cant do that, then do the 811/812 rig, as 811A's will modulate that fine.
Brett
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KM1H
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« Reply #20 on: September 25, 2009, 09:54:04 AM » |
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Depending on the driving power available the choice would be 572's or 813's. A good layout of the 572B's in parallel along with around 47-100 Ohm 2W carbons in the grid leads should eliminate the need for neutralization as a 80M monobander.
Also when feeding the bias use a roughly 3000 Ohm 1W resistor across the feed RFC. This eliminates any chance of a TPTG oscillator.
Another tube choice is the usually ignored 803 which are at the low end of the price range on Epay and hamfests. They can take a beating.
Carl
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KC4VWU
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« Reply #21 on: September 25, 2009, 01:55:30 PM » |
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I was figuring with the 572B's, I wouldn't have to worry with the screen supply either. I could also modulate them with a pair of 811A's using the ART-13 mod tranny I have on hand. I'd also prefer to use pi-net on the output. Anyone have some schematics I could smoke over?
Phil
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Steve - WB3HUZ
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« Reply #22 on: September 25, 2009, 02:04:40 PM » |
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I'd flip the tube complement - 811s in the final, and 572s in the modulator. But I like a lot of audio. |
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KM1H
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« Reply #23 on: September 25, 2009, 07:22:55 PM » |
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Ive heard the ART-13 iron cant take more than 200-250W on a good day? Also dont hang any high level clipping or other junk on the secondary that can reflect back to the primary. Don has commented on xfmr failures recently on here or QSO.
Carl
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KC4VWU
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« Reply #24 on: September 25, 2009, 08:14:23 PM » |
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If that's the case, I think I have one more mod tranny that might work better. I'll be honest, I can't afford to ruin anything; literally. Work has been pretty slim for most of this year and we've been working an average of 6 days a month at the plant. I'm really fortunate that I have collected a lot over the years, so at least I do have things to play with in my newly acquired spare time.
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