Oddball Amp by an Oddball Hacker.

[DummyLoad]

I may actually build this. Just killing spare time experimenting with compactrons & other TV/Radio oddities. Sounds pretty damn good for something just cobbled together.

First iteration had no reverb, so i was wondering one day if I couldn't spice things up with a 1 tube reverb using compactrons - I was more or less successful in that endeavor using a 6MF8, but ran into issues with hum that I initially thought were related to the tube I selectected, however,  that was actually unrelated to the tube -  More on that later.

So, assuming the 6MF8 was the issue, as the internal shield connects to Kath/G3 of the power pentode, I subbed in the more rare audio purposed compactron, a 6T9. The 6T9 has a hi-mu triode and basically a 6AQ5 in the same envelope, however, the internal shield is brought out individually to a it's own pin allowing us to ground the internal shield. This STILL didn't resolve the hum issue, so after some head scratching, I started swapping out tanks and viola! it was a grounding issue on the tank. The way I had grounds connected on my breadboard, the input isolated tank (Fender style) was prone to picking up hum. Great! There's where we stop, right? Oh hell no! This thing is supposed to be low-cost to re-tube, right? and with the fact that the 6T9 is becoming scarce and copies are pushing $20 each., I could go back to using the 6MF8, but that's was really overkill (15W plate power pentode to drive a reverb tank is like a 454 chevy in Vega 2dr hatchback), I pressed on for an alternative to the 6T9.

What to do? Enter Version 3. (actually rev 6) There is a triple triode that has all three triodes that are similar, that doesn't cost a small fortune (think 6C10, a triple triode 12AX7 used by Ampeg and one Fender), this tube has characteristics that are quite similar to a triple 12AT7 and doesn't  drain the wallet - Enter the 6AC10. I strapped 2 sections together a-la Fender and used the third section as the tank recovery amp. This thing sounds beautiful, makes about 20W and was a lot of fun to bring to life.

Possible Rev. 7 - I ditch the 6AY11 for a 6AC10, two of the sections become the LTPI and the third section a LFO for tremolo. Maybe. Thoughts?

--Pete

       

[tdvt]

Thanks for posting this.

Not really familiar with the compactron tubes but I can see they would offer up a lot of possibilities.

Price tag on the 6C10 is a wet blanket though. But the 6AC10 seems like a perfect fit for the Fender reverb circuit.

Did you have 12-pin sockets already on hand?

[shooter]

like a 454 chevy in Vega 2dr hatchback

Mom let me borrow here small block Vega when I was home on leave, some moron, running a stop sign, T-boned me at 60+mph.
Dad n me towed it to his buddies place, he wanted the front spindles and a few other parts for his drag car, a 454, super-charged Vega, turned 8's in the quarter mile!  Mom got a new Chrysler 

Sounds pretty damn good for something just cobbled together

let sleeping dog lie if they're happy

[66Strat]

Mom got a new Chrysler 

Was it as big as a whale? Did it seat about twenty?

Be sure to bring some juke box money.

[AmberB]

Mom got a new Chrysler 

Was it as big as a whale? Did it seat about twenty?

Be sure to bring some juke box money.

Tin roof, rusted!

[AmberB]

This is a pretty cool thread!  I've been wondering about using compactron tubes for years now, but it's been hard to find much info on their use in audio amps.  I had to write down the the tubes Dummyload talked about so I can check my stash to see if I have any.  I have 12 pin sockets from 7868s when I pulled them from Bogan amps to put in octal sockets for 7591s.

One thing I was wondering about, in the schematic for the amp in question, he uses a 6AV6 and a 6AU6 for the preamp.  I know that there are several tubes that have a high mu triode and a small signal pentode in the same bottle, they're normally used in the vertical section or the video section of tube type TVs, perhaps one of those tubes could be used in place of the 2 separate preamp tubes?  Just a thought, since the amp already uses other non-standard tubes...

[PRR]

> like a 454 chevy in Vega 2dr hatchback

That was a go-to-school car when I was a boy. (OK, when my little brother was a boy.)

Wild "overkill" was more like this:

[DummyLoad]

Mom got a new Chrysler 

Was it as big as a whale? Did it seat about twenty?

Be sure to bring some juke box money.

Tin roof, rusted!

Tin Roof - Busted! - Meaning she got knocked up?

[shooter]

Meaning she got knocked up?

now we're getting a 'lil personal!
 Dad said I was brought to life in a '53 Chevy, he wasn't sure which seat!   

[72Blazer]

That reminds of the song "Night Moves" by Bob Seger

[66Strat]

Tin Roof - Busted! - Meaning she got knocked up?

I always thought it was rusted.

https://www.dictionary.com/e/wp-content/uploads/2018/11/tin-roof-rusted.jpeg

On another note, would the correct pronunciation of Rock Lobster in Maine be Rahk Lobstah?

[DummyLoad]

Tin Roof - Busted! - Meaning she got knocked up?

I always thought it was rusted.

https://www.dictionary.com/e/wp-content/uploads/2018/11/tin-roof-rusted.jpeg

On another note, would the correct pronunciation of Rock Lobster in Maine be Rahk Lobstah?

You're correct - My apologies. 

Yes, I used to live in Massachusetts . It IS as state Rahk Lobstah! The live version of that song is my favorite.

&ab_channel=RHINO

--Pete

[DummyLoad]

  I have 12 pin sockets from 7868s when I pulled them from Bogan amps to put in octal sockets for 7591s.

With 7868  you have 9 pin NOVAR sockets left over.   

One thing I was wondering about, in the schematic for the amp in question, he uses a 6AV6 and a 6AU6 for the preamp.  I know that there are several tubes that have a high mu triode and a small signal pentode in the same bottle, they're normally used in the vertical section or the video section of tube type TVs, perhaps one of those tubes could be used in place of the 2 separate preamp tubes?  Just a thought, since the amp already uses other non-standard tubes...

That would probably a bit of challenge to keep stable - High mu triode and very high mu pentode in same envelope with supporting circuitry such close proximity may be difficult if not next to impossible to manage. Just my 2cents.


--Pete

[AmberB]

With 7868  you have 9 pin NOVAR sockets left over.   

DOH!  You're right, I was thinking of socket size...
I did order some 12 pin ceramic sockets several months ago because I was thinking about trying a triple triode.