RE: Genuine '51 Fender 5A3 pics and info.

[Carlsoti]

   This thread is really just for reference and by request. I'll post the pics and relevant info on subsequent posts. For now, the short(ish) story of how it ended up on my bench.

A few weeks back, I responded to a Reddit post about "What circuit is in this old amp?" It was an amp the OP's grandfather bought new and gigged extensively for two or more decades before it was retired, and it was left to him over decade ago. Since then, it's been in the back corner of the closet of his childhood bedroom.  It's a TV front Tweed Deluxe, which means if it's stock, it's a 5A3. I stretched my neck out on my original reply, telling the OP "If you're near me, I'd love to get that heirloom amp up and running for you!" As luck would have it, he lives just a few miles away! After talking with him about it for a bit, he made it clear he didn't want or need fancy NOS coupling caps, mojo infused filters, etc. He just wanted it to work so that he can safely use it at home, for sentimentality's sake. I quoted him $100 to do a 3-wire grounded plug and (not fancy)electrolytic caps, pot and jack maintenance, and a good once over to gauge it's general health and ability to handle modern mains voltage. I also informed him that I was concerned about leakage through the coupling caps, but I'd wait to see what the voltages looked like.
    As it sits now, I've put Mod 16uF 475V electros in. Bias was up at 100%, with a 10% difference between the tubes. After that, the leakage of the last two coupling caps was something like 0.375V and 0.16V, so i swapped in some .047 Mallory 150s. Currently, I'm waiting on a NOS 5Y3 and a pair of burned-in and matched JJ 6V6S, selected by current for a bias around 80% for future-proofing against high mains. Once I pick those up, I plan on recording voltages throughout, varying the mains from 108 up to 123VAC.  More to follow...

[Carlsoti]

More pics...

I'm struggling to get these pics uploaded here. I think it might be better if I put them up on google and link it back here.

Let me know if there are certain parts of the circuit you want to see up close.

[tubeswell]

Installed wiring gutshots incl control panel and sockets please
And exterior cab and control panel shots (and overall cab dimensions and tube chart) please.
And transformer shots and codes (and speaker basket and cone codes)



TIA

[Carlsoti]

I hope I did this right. If I did, here's the link to the pics on my google drive.

https://drive.google.com/drive/folders/1TJUNJfeddUjU1mzCh7iBXVhx_XFYD6zn?usp=sharing

If I didn't do it right and opened myself up to being hacked or scammed, please let me know. TY!

[tubeswell]

Viewing doesn't seem to be enabled

[sluckey]

Download. A 195MB zip file will be created and downloaded to your computer.

[tubeswell]

Awesome - working for me now. Valiant! Many thanks. Hugely appreciated

[moosetone]

Thanks for sharing!

[Carlsoti]

I just realized that the black, .005uF 600V cap across the power tube grids is likely not stock. It seemed like this amp was really dark and kinda quiet. Most of the reading I had done on it compares it that way in contrast to the later 5E3. Also, the amp sounded really great cranked up. Still, I couldn't shake the feeling that it just didn't sound quite right. This amp is from the lap/pedal steel era and where clean, clear, and bright was the name of the game and distortion was still seen a BAD! I pulled one end of that cap and it immediately made a huge improvement. The proverbial "wet blanket" was removed. Of course, the high-end hash of 70+ year old carbon comps is also now more readily apparent.

I won't have a chance at a high volume listening test until later this afternoon, but thought I should mention it to anyone looking at the pics for reference.

[dude]

Very nice, thanks for great pics. I wonder if  replacing those old coupling caps would have an effect on the tone, better or worst..?
It’s a vintage amp.., does one leave it as is, or replace a 70 years old cap..?

[tdvt]

As the others have said, many thanks for sharing/posting those pics.

[tubeswell]

I just realized that the black, .005uF 600V cap across the power tube grids is likely not stock.

It may not be on the schematic, but who knows whether they added it at the factory for someone (as a noise floor cure?)? The cap looks fairly antique-ish.

[Carlsoti]

I wonder if  replacing those old coupling caps would have an effect on the tone, better or worst..? It’s a vintage amp.., does one leave it as is, or replace a 70 years old cap..?

In this instance, I put in all new electros, but I only changed 2 coupling caps. They were allowing 0.371v and 0.140v to get to the 6v6 grids. It was already biased at %100, so I felt it would be a benefit to the longevity of the amp to swap those caps. After the change, they were 0.01v and 0.009v. I also showed no voltage bleeding past the input caps, so those stayed. Most of the caps were really near 20% over-spec. I can deal with a coupling cap with no leakage that measures .06 instead of .05uF. In the end, the customer went with my suggestion of a NOS 5Y3 and new set of matched tubes, which brought the bias down under 90% at 123VAC input.

I'm not a big believer in MOJO, but there are certain combinations of old, worn out parts that can sometimes just sound somehow better. If the parts function safely and properly in circuit, I try not change things all willy-nilly, particularly in desirable amps.

[dude]

That’s why old vintage amps of the same can sound different, components drift.

[Platefire]

Very Interesting! Thanks for the bit of history on the original owner. I couldn't help but wonder what kind of music the original owner played.
That was probably the ideal gigging amp for those days being a 1-12 combo(easy portable) with PP 6V6 power for a little bit of volume. Thanks for sharing!