60's Vintage TNT Bass Amp

[Enzo]

Obviously this is all opinions floating around. But why do the hole plugs "look original"? Their very presence looks unoriginal to me. We have seen the photos of the amp as originally sold (presumably) with all the control and jacks in place.

[Archie Speed]

Very little info so far on this amps origins. TNT Electronics, Venice CA. The late Frank Cooley & family built these in the late 60's & 70's. Some in their garage. Canned Heat is said to have used these around the Woodstock period.

So this has some historical significance as a So. Cal. 60's boutique amp. I'm still looking at the history & I'm never in a rush to do anything, mod or otherwise. What's there looks a lot better in pictures than in person. I'll try to refine my schematic sketch so that it is legible & decipherable & post when I do.

[trobbins]

Steven Quick's amp is a different amp. The cabinet has same piping style, but no half-slope front. PCB appears more 'refined' with designators, but not on all parts and lettering is cut-off. Top panel layout is 'better' in terms of weight distribution and cooling of valves. Rear panel appears to have same mains voltage selector (?), plus a fascia. All good pointers to a later model/manufacture.

[Archie Speed]

S. Quick's amp looks like a squared cabinet, fully loaded (norm & bass channel) newer, neater & better produced version of what sits before me. Same faceplate, different chassis. Read panel is just a receptacle.

I tore into this a bit tonight. Take a Bassman AA/AB165 schematic, dump the #2 & 3 pre 12AX7 sections & change the 6L6 power section to reflect splitting off to the 4 ea EL34's & that's it. Very few deviations from the Fender schematic (only a few values & location changes).

Justin - I'll do some searching for the Earth Amps schematic you mentioned. Jumped channels bring good things to life. I mentioned the 'AA' version earlier because (as I recall) it was the last version before CBS came in & changed things. It kept the AA864's power section but added the AB preamp improvements. Close enough to what is existing in this head right now.

What is existing is dangerous just to look at. Lotta work no matter what I do with it. But...I believe that I can do a rebuild that can include enough good stuff to make it close to original & have some decent additions without desecrating the original concept.

[Enzo]

We can talk about beaters and prototypes, but even your old half-an-amp was far enough along for them to have a 3-D logo badge on the front.

Even the quick amp has surplus inside. Note the two part boards are different, one has turrets,the other uses eyelets. Those component numbers look like they belong to something else, not the amp circuit. Seems unlikely a simple amp like a Bassman would have component numbers like R7035.

I'd be willing to bet my lunch money this this was originally a straight Bassman clone. Maybe a tiny tweak or two.


Earth Bass 2000:
EARTH ISC AUDIO B 2000 SUPERBASS TUBE AMPLIFIER SCH Service Manual free download, schematics, eeprom, repair info for electronics

[Enzo]

Oh, Elektrotanya also has the guitar version, G2000, which includes trem and reverb. And the PA2000, four channel tube PA head. I have one of those here, in bright blue sparkle tuck and roll.

[Archie Speed]

Thanks, Enzo.

[Archie Speed]

For anyone interested, & to the best of my ability, here is a schematic of what I've got before me:

[trobbins]

Standby switch will be secondary side HT CT connection.

Output screens don't look right, perhaps each one dropped from same power supply rail?

Feedback not right.

0V connection needed for bottom of LTP PI.

[Enzo]

LTP shows a ground connection through the parallel 100 ohm resistors, this make close to the 47 ofm resistor of a Fender. I think the feedback line then connects to the top end of the two 100 ohm, not the grounded bottom end.

The B+ filter caps are all upside down.

Agree the screens are not in series like that. The wire from the left end of the choke should than have a 500 ohm resistor to each screen individually.

At the ground end of the pair of 100 ohm, is a line going left, it then grounds out the B+ to the preamp. That line does not belong.

I suspect that 100 ohm cathode resistor in the input triode is not right. 1000 maybe?


On the other hand, it is possible this drawing is 100% correct, and the cobble job that is in the chassis was wired that way.

[Justin Thomas]

Might any of those "errors" explain the original symptoms: mains fuse blown & 2 EL34s showing signs of flaming? Might put to rest the "factory/modded" debate...

Justin

[Audiotexan]

Also noting that you listed EL84 as opposed to EL34 in the schems

[Archie Speed]

Fun to be old, huh? OK...thanks for the scrutiny & keeping me honest gents. I just started using TinyCad for this project, so I'm trying. My errors. My haste. Sorry for the confusion. I appreciate you taking the time to look & don't want to waste that precious commodity.

So...latest revision drawing:

Corrected polarity relationship of B+ fil caps.
Corrected feedback ckt routing.
Corrected value of cathode resistor V1a.
Deleted line at paired 100 ohm resistors.

The screens are what they are. Each octal socket has a 500 ohm resistor sitting across pins 4 & 6 and each pin 6 is daisy chained together.

Going once over & pulling wires again, I believe this latest to be as representative as possible. I left some of the lines long so as to give a representation of physical connect points as well as electronic.

[Archie Speed]

OK...one last effort for today. Corrected to show EL34.

[Enzo]

OK, now think about the screens. Pin 6 is not used by the tube, it is a handy point to solder something. If all the pins 6 are wired together, that means they are all on one line, then at each tube socket, a 500 ohm resistor goes from that lone over to pin 4, the screen grid. Your schematic does not have the pins 6 daisy chained. Your drawing has a resistor from pin 4 of V1 to pin 4 of V2, where another resistor joins to go to pin 4 of V2, and so on. Your description sounds correct, your drawing does not seem to agree with your description nor does it seem correct.


And it sure looks like half of a Bassman 100:
http://bmamps.com/Schematics/fender/..._100_schem.pdf

Note in your drawing the unecessary 0.1 cap from the plate of the second triode to ".22" resistor, I assume .22Meg, or 220k. That is left over from when they eliminated the master volume. And they used the 12AX7 version of the phase inverter, but those are details. This butresses my thought that it is a Bassman clone. Or once was.