Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frankenxtein on June 19, 2022, 09:07:39 am
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I acquired a couple PP 6bq5 Zenith amps on eBay.
One is the main unit like the schematic and one is the satellite for lack of a better word.
I was just looking for transformers "output" to be exact and stumbled on a deal under $200 with shipping for both amps sans the 6bq5's. I got the other tubes with them. Also , got the knobs minus one.
I'm not into having a "tube stereo" , no offense to those that are into that sort of thing.
The chassis are decent and I wasn't planning on changing the rectifier or power tubes.
Just wondering how much of the original circuit would be useful in making a couple guitar amps.
I'd have to recap these amps to feel good about powering them up as is.
They don't seem to fetch a special price when restored.
I was thinking something like 18wattSuperliteTMB and using 5y3 rectifiers.
The transformers physically appear to be the same in both amps , different serial and part numbers.
They seem to have the same DC resistance. The OT's might not be what I want in a 18watt amp.
The build dates are different and the preamps are different too. The satellite uses a 6at6 for V1. They both have the same phase inverter.
I would have to disconnect the OT's to see what the ratio's are on those. I've been helping my son's band so I haven't had time to do much in the way of building anything. Heck I just got a couple heads that I built into some cabinets.
Too many irons in the fire.
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> The OT's might not be what I want in a 18watt amp.
Why not? You don't get a big choice on EL84. 8K +/-20 covers all useful conditions. Zenith didn't over-size their iron; if you want tiny iron you should shop RCA or Silvertone consoles.
I'd keep the circuit 90% as-is. The front end wants less switching and more gain. The floating paraphase driver is uncommon in g-amps but works fine, more folks should try it. The 22k in the NFB loop could maybe be 47k or 100k for looser sound.
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> The OT's might not be what I want in a 18watt amp.
Why not? You don't get a big choice on EL84. 8K +/-20 covers all useful conditions. Zenith didn't over-size their iron; if you want tiny iron you should shop RCA or Silvertone consoles.
I'd keep the circuit 90% as-is. The front end wants less switching and more gain. The floating paraphase driver is uncommon in g-amps but works fine, more folks should try it. The 22k in the NFB loop could maybe be 47k or 100k for looser sound.
Thank you ,
On the contrary on the size of the OT's they're about the size of what they sell for a 5e3 (Hammond)
I was thinking larger :wink:
I probably get the wrong impression of what size is. :l2:
My hat size , feet and hands are big but , the rest. LOL
I had to look up paraphase. :icon_biggrin:
I'd have to probably rebuild that and was wondering whether it was useful.
It's truly shameful that I've got these amps.
Actually the CC resistors are pretty darn close. The satellite amp is probably where I should start.
It has less clutter and the same paraphase setup.
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Most of the small Supro amps have paraphase PIs, as well as the pre E3 Fenders. There are some very good sounding amps that have paraphase PIs.
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> I'd have to probably rebuild
Why? Don't knock it before you try it. It does need a stage of gain to cover the difference needle vs pickup, but an LPB is enough if you have strong fingers.
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> I'd have to probably rebuild
Why? Don't knock it before you try it. It does need a stage of gain to cover the difference needle vs pickup, but an LPB is enough if you have strong fingers.
Strong fingers :l2:
While I like point to point construction.
It's quite a mess inside but , it is possible to just restore the two amps.
Honestly that's not why I purchased them.
However the original circuit , phase inverter and feedback circuit caught my eye.
Getting the Satellite amp up and running should be easier.
Here's a link for that one.
https://www.dropbox.com/s/qpdmz2wroyt3ftm/radiomuseum-zenith-radio-corp-srs10-ch-5b24-60976.pdf?dl=0
Here's a link for the main amp.
https://www.dropbox.com/s/k679lfrb9w46c6n/radiomuseum-zenith-radio-corp-sf125-ch-5b23-605143.pdf?dl=0
Here's an actual photo of the underside of the amps.
https://www.dropbox.com/s/dyeijhy9tmtov33/zenithamps.jpg?dl=0
Here's someone that has a 5B23 recapped for sale.
https://www.ebay.com/itm/185427581333?hash=item2b2c585995:g:5BwAAOSwVg1h7Fm-