1961/2 Fender Tremolux 6G9-B restoration

[Bob-I]

Last week a friend of mine and guitarist in a cover band I play bass in, texted me that he bought this amp and asked if I’d look at it. My first reaction was “holy s**t what a find” then is said of course I’d look at it. I’ve been keeping his Hot Rod Deluxe running for years (not an easy task) so why not. It was very dirty so he cleaned it up best he could, plugged it in and promptly got zapped, but everything worked. The PO said it had been re-capped and there was a piece of masking tape with a 1990 date in it.

I bought it home after the gig Saturday, pulled it apart and checked it over visually and with a simple multi meter.

The re-cap was not complete or correct. Under the doghouse there was a pair of 80uF in series on the first node, and 3 47uF caps for the rest. Inside the original bypass and C- caps were still there. There doesn’t appear to be any changes inside at all.

The rectifier tube is a Mesa branded GZ34, output tubes, big bottle Mesa branded 6Ls, and the 4 12AX7s are a mix. I’m hoping those big bottles are still good, but the 12AX7s are nothing special.

I ordered Mod 20uF/500v caps for the doghouse, 25uF/50v for bypass and C-, metal film resistors for screen and PS, and a bunch of carbon comps as some measure way off.

I recorded my initial evaluation with my hat cam, sorry for the dizzy recording, and I’m not a tech so forgive any mistakes.

No questions, I just thought it would be an interesting thread.

https://drive.google.com/file/d/1Tw7sai ... p=drivesdk

[pdf64]

Nice!
It may be a 6G9, maybe the 6G9B
https://el34world.com/charts/Schematics ... _schem.pdf

[Stevem]

Please note that most of today’s Mesa’s GZ34’s / 5AR4’s are more of a 5Y3 as you can clearly see just by comparing the size of the plate structures in each.

The Mesa tube will output less B+ then a real GZ34 and I am not really sure if it will handle what a real GZ34 will handle in terms of first filter node Uf value.

All of this means that the amp will not sound like it should and if the amp is played loud enough to have the B+ sag then the Mesa tube will not live the life that a real GZ34 would.

Even the glass bulb of the Mesa tube is that of a 5Y3 rectifier.

I am not saying this is all a bad thing as it may allow for its new owner a more gig friendly volume where the amp starts to allow the output section to clip.

Do you have a O-scope?

Some of these model Fenders I have seen oscillating at volume above 6 or 7 and you will 1) need a scope to see it and 2) need one to fix it .

[Bob-I]

Nice!
It may be a 6G9, maybe the 6G9B
https://el34world.com/charts/Schematics ... _schem.pdf

Yeah, typo, it’s a 6G9-b

[Bob-I]

Please note that most of today’s Mesa’s GZ34’s / 5AR4’s are more of a 5Y3 as you can clearly see just by comparing the size of the plate structures in each.

The Mesa tube will output less B+ then a real GZ34 and I am not really sure if it will handle what a real GZ34 will handle in terms of first filter node Uf value.

All of this means that the amp will not sound like it should and if the amp is played loud enough to have the B+ sag then the Mesa tube will not live the life that a real GZ34 would.

Even the glass bulb of the Mesa tube is that of a 5Y3 rectifier.

I am not saying this is all a bad thing as it may allow for its new owner a more gig friendly volume where the amp starts to allow the output section to clip.

Do you have a O-scope?

Some of these model Fenders I have seen oscillating at volume above 6 or 7 and you will 1) need a scope to see it and 2) need one to fix it .

Thx Steve, and yes I’m aware of the GZ34 being a 5Y3. I didn’t know about comparing the plates, I’ll check that out. I think the 40uF reservoir is pushing it with modern tubes, I have a few NOS 5Y3s which tend to hold up well.

Yes I have a scope and will check for PO, good point.

[Bob-I]

Please note that most of today’s Mesa’s GZ34’s / 5AR4’s are more of a 5Y3 as you can clearly see just by comparing the size of the plate structures in each.

I compared the Mesa branded GZ34 to both a NOS RCA 5Y3 and. New JJ GZ34. The Mesa plates are bigger than both, leading me to believe it’s either a real GZ or a more robust 5Y3.

I’ll be installing 2 Mod,20uF/500v in parallel. We’ll see how the Mesa holds up.

[Stevem]

Well that's good, I guess Mesa has stepped up there game!

[Aaron]

Nice project and great amp!
I got one last year that had replaced PT and OT. As well as having some weird boost board installed. But the circuitboard and pots hadn’t been touched.
I removed the mods, gave it a service and installed some Hammond transformers. Perfecto! One of my favourite amps.

Aaron

[Bob-I]

Nice project and great amp!
I got one last year that had replaced PT and OT. As well as having some weird boost board installed. But the circuitboard and pots hadn’t been touched.
I removed the mods, gave it a service and installed some Hammond transformers. Perfecto! One of my favourite amps.

Aaron

Looks great Aaron.

Looks like you replaced the domino caps in the tone stack. I’m hoping to save them, but if they’re out of spec or leaking DC I’ll have to.

The parts order should arrive Monday then I can get to work.

[Bob-I]

I’m an idiot…I ordered a 50uF/50V electrolytic for the bias supply. With the new diode and higher wall voltages, the voltage across that cap is over 60V.

So I ordered a 100v cap and a 10k pot so I can adjust the bias.

Everything else seems good. New AC cable, filter caps (500V, it’s measuring 460 unloaded), plate load resistors, screen grid resistors.

When I get the correct bias supply filter cap I can put in tubes and fire it up.