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Old 6th December 2010, 03:27 AM   #1
AF Froger is offline AF Froger  United States
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Default Newby here first post.

I've purchased a few old tube type police transeivers from a local Ham Fest.

The transmit sections use an 829b as an RF final. The tube data says it can be used as an audio amplifier.

Has anyone had expiriance with this tube as an af amp? I'm thinking guitar amp here.

I know this is an odd aplication, but its just one of those fun junk box project ideas.

Thanks for any advice.

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Old 6th December 2010, 04:29 AM   #2
bob91343 is offline bob91343  United States
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Those are great tubes! They are roughly equivalent to a pair of 6V6's in one envelope, with the nice plate caps. You can certainly make a guitar amplifier from one in push pull.

I used one for many years in a ham radio transmitter, running 120 Watts input Class C. I had 750 Volts on the plate, and about 250 Volts on the screen. You can wire the heater as 6.3 V or 12.6 V.

The sockets could be hard to come by so try to salvage those. The plate connectors often would have heat fins on them.
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Old 6th December 2010, 05:20 AM   #3
db! is offline db!  Canada
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Pete Millett has built an amp with the 829b; IMO, it's somewhat complicated unless you have some experience with tube amps...

829B Amplifier

Last edited by db!; 6th December 2010 at 05:23 AM.
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Old 6th December 2010, 05:42 AM   #4
aardvarkash10 is offline aardvarkash10  New Zealand
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go pentode - it won't do triode well and can't do ultra linear

For geetar, I'd parallel the sections and go SE. Not hard to drive either.
"It may not be easy for some to not hear differences, even if they are not there." - Vacuphile,
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Old 6th December 2010, 04:58 PM   #5
AF Froger is offline AF Froger  United States
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Thanks for all the quik and freindly responces. Here is the plan, correct me were I may be going down the wrong path.

I have a very nice vintage UTC opt. The thing is 5LBs, specs on the side says type LS-52, 8k ct, 20 watts max, 7 hz to 50khz. I think the 8k may be low acording to the 829b data sheet but all I'm looking for here is 10-15 watts. Since this is a guitar amp distortions not an isue. Its actuly desireable.

So PP it is. Thinking 450 v to the plates, 225v to the screens. Not sure about the neg, bias on G1? Data sheet says -36v but thats at much higher plate HT volts.

I'm thinking of using the Fender style phase inverter. Allthough I have a very nice vintage Peerless interstage transformer with a 10k primary and 40k ct secondary. Its a fairly husky 1 LB, side panel one this says 200hz to 20khz at +- 15 DB. I want to use the global feed back precense control Fender uses but not sure how that can be addapted to the use of a driver transformer. Fender uses a long tail phase inverter.

I'm thinking about using a 10 Ohm resistor on each plate to make plate curent balance measurments. I'll use a seperate bias pot per grid if I go the Fender phase inverter. Not sure how to do this with the driver transformer?

I will salvage the sockets and plate caps from the police radios.

You guys are a great wealth of ideas and info.

Thanks again.

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Old 6th December 2010, 05:38 PM   #6
TheGimp is online now TheGimp  United States
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You can apply the feedback to the cathode of the tube driving the transformer if you want it inside the feedback loop.

Otherwise apply it to the cathode of hte LTP.
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Old 6th December 2010, 05:44 PM   #7
taj is offline taj  Canada
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It looks to me like the OPT is better suited to Hi-fi. Part of a guitar sound includes the limitations of cheap-ish transformers. I guess it really depends on the type of guitar sound you're after. That OPT would be nice (but still overkill) for a jazz guitar amp.

interstage: 200hz to 20khz at +- 15 DB
Really? Is there a chance that might be +-1.5? I shudder to think of what the f-3 frequency would be on the low end if -15 is at 200 Hz.


Last edited by taj; 6th December 2010 at 05:58 PM.
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Old 7th December 2010, 01:45 AM   #8
AF Froger is offline AF Froger  United States
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Yep it says +- 15 DB. Thanks guys. Found a good PT in my junk stash.

It has 2 HT secondaries. No load one measures 170 vac each side of ct. The other measures no load 365 vac each side of ct. Its a big heavy thing. Sould have plenty MA. for this project. It has a hefty 6.3 v for fills and a 5 volt for a 5u4 ect. I'll use a 6x5 for the 225 volt screen supply.

Thanks again guys. I'll let you know how it goes after the smoke clears LOL.

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