Fixing up a 50s homemade tube amp

Johnny-B

I was given a chassis of a 1950s home made tube amp without any tubes. It has octal sockets for a rectifier tube, 2 pentode preamp tubes, one dual triode phase inverter and 2 output tubes. So I used a 5Y3 inverter, 2 6SJ7s, a 6SL7 and 2 6V6s.
At first try there was horrible 50Hz mains hum. I replaced the electrolytic caps in the power supply chain, plugged the tubes back in and it works but is distorted even at low volumes.
The bias is way off on the preamp tubes causing almost no clean headroom. Perhaps the builder used some other preamp tubes.I will rebias them and see if I can get some clean headroom. I have a 275 V supply on the preamp plate. My calculations suggest and 82k resistor in the plate feed and a 2k5 in the cathode.
If I knew how to post photos, I would!

V8

Johnny-B Heya, pics always welcomed!

Here's the current way :: https://community.guitartalk.co.za/d/4055-how-to-post-pictures-t4055/2 - let us know if that isn't working! 👍️

I was playing on a old RCA tube amp that was originally was the companion audio amp for a film projector - sounded great with the right guitar (oddly it loved humbuckers)

guidothepimmp

This will be great.. these things turn out as great guitar amps

Johnny-B

Adding pictures not working. No additional options

V8

Johnny-B No worries, thanks for the update, I'll dig into and see what's up with that. 👍️

V8

Johnny-B Heya J, my apologies - I steered you to old info 🤦 here's the actual current way : https://community.guitartalk.co.za/d/26380-how-to-post-pics. Also, Norio allowed larger files sizes after he wrote that post, so unless it's a truly monsterous image, you shouldn't need to resize.

I'v just tested with 'Meme of the year' post, all worked as hoped.

Johnny-B

Here are some pics of the 50s home made amp

Note the output transformer and some of the capacitors are branded "Wild & Marr". I've converted the one pre-amp pentode to triode mode with much lower gain of =/- 20 to give me a clean channel. I'm busy making amp and speaker housings at the moment from 6mm MDF that I had left over from making cupboard doors. will post more pics when finished. I want to use a plexiglass front panel with inverse decals on the back for input, volume, etc and then spray over the back. Does anyone know of a print shop that could make these?

guidothepimmp

Johnny-B
Dont know of print shops per se, but if all else fails, you could probably approach a laser printing setup and get it done that way

guidothepimmp

Sweet.. looking good

Johnny-B

Have been working on the cabinets. Still need to get the face plate. A friend in the printing business is designing and making a plexiglass face plate for me. But so far,
so good.

V8

Johnny-B Looks great! The handles and tweed are really pro touches 👍️

guidothepimmp

That looks excellent. Nicely done. A real looker

Johnny-B

Thanks for the compliments. Handles from Gelmar - not expensive. Tweed left over from building 5E3 Tweed Deluxe!

Johnny-B

Here are a couple of pics of the final _Fifties _Special__amp and cab

V8

Johnny-B Finished up sweetly, nice job! How does it sound?

Johnny-B

I'm really impressed with the sound. The rhythm channel is clean with nice chimey highs and solid bass, whilst the lead input provides great overdrive. It also seem to take pedals well.
I'm now servicing and repairing amps and guitar electronics. Is there a place on GuitarTalk that I can advertise?

V8

Johnny-B Is there a place on GuitarTalk that I can advertise?

Yes!

Here's the section : https://community.guitartalk.co.za/t/general-classifieds

Also there is a fairly active whatsapp group (at least compared to the forum) if you'd like a invite, let me know.