I wanna start a new project utilizing some spare tubes. 6AC10 & 6AQ5A's

[HoodratShinobi88]

Hey all! Doubt that much of you remember me its been like five years since I frequented the site. My old username was something like trialbyguitar but ive since forgotten it. Before I quit messing with these things you guys helped me build a pretty cool schedule 40 variant using a 60's record player, russian OTK2 (12ax7 w pins9&1flopped) preamp tube and a single el84 rectified by an EZ81. Its been my recording amp since & and interesting conversation piece. But once again the urge to build has overcome me. I wanna slowly build a larger higher wattage amp using mostly the tubes I have laying around. However, I forget alot of my tube amp knowledge  I have 7 6AQ5A's 3 6AC10's 2 6CG7's 3 12au7s another EZ81 and a shitttttton of those russian tubes (6N2P I think..).can any of you help me come up w a schematic that would utilize like a pair of the compactron's and four or even six or eight of the 6AQ5A's? I had a schematic drawn up for a compactron pre-amp I started build as a pedal and scrapped but I cant find it right now.This projects gonna serve as a refresher for me any help would be greatly appreciated. I should mention that this gonna be a slow build, I wanna work from the tubes out using everything I have and buy a suitable PT last..

-Tyler

[kagliostro]

For compactrons there are some info and projects here

http://www.junkbox.com/electronics/CompactronTubesIndex.shtml

Kagliostro

[HoodratShinobi88]

Very cool, I actually came across the page a little earlier. I love compactrons, I'd like to try my hand at one of those squirrel monkey single tube amps after this proj. Anyone have a schem for like a 8x6v6 amp that I could adapt to my preamp design? I'm pretty sure I have it saved on another comp or can just come up w a new one.

[stingray_65]

A push pull parallel power section of 6AQ5's would put you in the 3.5-4k ohm realm. so there would be a lot of Fender OT's for you to choose from, I'm guessing in the 20-30 watt range.

for the PT keep it at about 300V and maybe 150mA.

for the heaters you'll need 5.2 amps minimum, that will be big iron, to heat up 2 compactrons and 4 6aq5's.

Basically you're dealing with 3 12AT7's and 4 6V6's

Base your design around a known good circuit that uses those parameters

Ray

[kagliostro]

This is a 3 x 12ax7 + 6 x el84 tube amp

https://taweber.powweb.com/store/6m50tmb_schem.jpg

https://taweber.powweb.com/store/6m50tmb_layout.jpg


and attached there is a layout for the Monkey Squirrel
(pay attention to revise - especially  the power supply)


Kagliostro

[DummyLoad]

fender super champ used 6C10 - 3 AX7 like triodes in one envelope with a P-P 6V6 output stage w/ reverb. 6C10 was used for summing amp, split load PI, and reverb recovery.   IIRC it is/was a well regarded little amp and made only for a short while. maybe a super champ like amp is just the ticket; you have most of the ingredients.

6N2P - 1st & 2nd stages.
6AC10 - summing amp, reverb recovery amp, cathodyne. (just like fender super champ plan)
6AC10 - 2 triodes strapped in parallel for reverb driver, third section for added tremelo osc. (may not have enough gain?) that wobbles 1st or 2nd stage.
4 x 6AQ5 for output stage - should get you about 20W into 4K-5Kohm load. or 2 x 6AQ5 for 10W into 8K-10Kohm load.
SS recto. save the EZ81 for a rainy day or use it in a 2 x 6AQ5 plan.

http://www.el34world.com/charts/Schematics/files/fender/champ_super.pdf

a little more legible copy...

http://www.freeinfosociety.com/electronics/schemview.php?id=917


--DL

[HoodratShinobi88]

I love how fast you guys are able to help me put my random ideas into some sort of concrete form:) I'm going to base my design upon the Weber amp, Seems to be less complicated to me and I have a line 6 amp I use when I want effects(rarely). So this is modified schem, showing off my awesome copy and paste skills. It made the most sense to me to use a single compactron for each of the channels,I don't think this effects the design of the amp even tho the original had both channels sharing V1. If you look at the 1.5k resistor tied to pin 6 of the first channel there is a little arrow next to it.in the original schem it says adjust resistor value for best tone, should I just throw like a 1k resistor and a 500 ohm pot in its place? I think it looks like I adapted this correctly but extra eyes never hurt. I'm gonna the hunt for a suitable chasis tonight.

[HoodratShinobi88]

http://cgi.ebay.com/THERMADOR-POWER-TRANSFORMER-760VCT-220mA-6-3-5A-5V-3A-/390293991051?pt=Vintage_Electronics_R2&hash=item5adf55ae8b&autorefresh=true I'm guessing this is overkill but im bidding on it anyways, would be cool to have for <$20

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=170612952496&ssPageName=STRK:MEBIDX:IT
bidding on this one too, even tho I'm guessing it doesn't have enough amps for all the heaters. maybe I could use it just for the heaters on the power tubes and grab one of those tiny 6.3's for the preamp tubes. hmm..

[kagliostro]

with the first transformer if you put SS rectify you are in order of 530v - ok for BIG bottles, not little amp.

Here is the layout for the Super Champ, if you need

http://www.superchamp.dk/papers/Super%20Champ%20Wiring%20Diagram.jpg

and a furtherly more readable schematic

http://www.superchamp.dk/papers/Schematic_SC.jpg

Kagliostro

p.s.:   Many thanks to DummyLoad, I didn't know the Super Champ, before I know only there was a Fender with a compactron, but didn't know wich one

[moonbird]

Here is an interesting boutique amp that uses the 6AC10 -- would love to know how they do the hi/low power switch trick.

http://www.mackamps.com/gem-head-combo/

[PRR]

> there is a little arrow next to it.in the original schem it says adjust resistor value

R36 1.5K will cause gross distortion; the cathode follower will work as diode not follower. R17 is also low. 5F6a uses 820 ohms and 100K; Weber doubled the first and halved the second. I'd suspect 470 ohms or less at R36 for "clean", and it may still need R17 more like 100K. Then perhaps add 1K trimmer to R36 to dial in your dirt.

Massive parallel output stage:

Max G1 resistance for 6AQ5 is 0.5Meg, 500K. PER TUBE. SELF-BIAS. _100K_ per tube fix-bias.

There is NOT a lot of point running 6AQ5 in fixed-bias. The plate voltage rating is not high enough for over-volting. Yes, 6AQ5 are still cheap so you could abuse them, but you seem to favor using tubes in hand rather than designing for the market.

With three grids parallel you are supposed to scale accordingly.

With SELF-bias (cathode resistors): Allowing for the extra 5.6K in each grid, R10 R11 should be on the order of 198K, not 470K.

The max grid resistance allows for a leaky grid. It is unlikely you will have three tubes at maximum leakage. Also you tend to bias fix-bias guitar amps well below maximum dissipation, so a little leakage won't incite a melt-down. Fender amps often violate the max grid resistance rating.

OTOH, one VERY leaky tube could pull -three- tubes into trouble. All eggs in one basket kinda failure.

If you make R10 R11 more like 220K (and increase C2 C3 for similar bass limit), then this driver can easily pull the load.

In FIX-bias: even if your bias-supply impedance is as low as 25K, you can't have "any" resistance at R10 R11, and that can't work. With a zero-impedance bias source (100K-5.6K)/3= 31K at R10 R11. Yes, you can cheat this to 33K even 47K. But now the driver has a very heavy load, will need re-design to be able to slam the 6AQ5 grids.

That's by-the-book. We know Fender often got away with 220K where the book said 50K. Still I think -three- fix-bias grids parallel is extreme, and 6AQ5 will make as much power in self-bias as fixed-bias if you semi-respect the 275V max plate voltage rating.

[HoodratShinobi88]

Thanks! foolish of me to think I could just attach this schem to different tubes and it'd work because they obv. have the same ratings   
you've got me a bit confused on the last part isn't this amp already self-biased? I thought those 5.6k resistors were cathode resistors. Looks like i've got a lot to relearn 

[Willabe]

No, the 5.6k resistors are the grid (control grid 1, pin 1) stoppers. Pin 2 is the cathode on this (6AQ5) tube, which is grounded (so not cathode/self bias)in the schmo.

The -B supply for fixed bias, is not shown, but would connect to "G" at the 2 - 220k grid return resistors.


           Brad            

[HoodratShinobi88]

http://www.blueguitar.org/new/schem/vox/ac30_pwr.gif so ive learned that the ac30 is fixed bias I think im looking at these 100k resistors that chain up and go back to the power supply? lol please excuse my inexperiance, how would i go about doing this w my idea?

[Willabe]

http://www.blueguitar.org/new/schem/vox/ac30_pwr.gif so ive learned that the ac30 is fixed bias I think im looking at these 100k resistors that chain up and go back to the power supply? lol please excuse my inexperiance, how would i go about doing this w my idea?

No, that amp is cathode/self bias. The resistors are 100R, not 100K and are the screen grid resistors (grid 2) which is why it is hooked up to the B+ supply.

The cathods are wired to the 50R/25uf that are in paralel with each other and go to ground.

Dougs library of tube amp info. has a lot of very helpful reading, which will help you understand where your getting stuck.                  Spend a little time in there reading, I think you'll like it.


                      Brad              


        

[HoodratShinobi88]

lol thanks Brad. I've read through it before & had issues understand but I think I finally got it. Lemme just be sure tho, I build a circuit like the one on the top left of the bias circuits page& it attaches to G just like where the 2x 220k's and caps are on the page & I have an adjustable bias amp? Then once its attached I check the voltage at g or at the plates of each tube and adjust the pot till its <275 I can do that for this schem without change any other resistors values or anything and this amp will work? just wanna be 100% before I start piecing it together.  thanks for your patience guys.

[HoodratShinobi88]

I know I just stick four diodes in there for ss recto.

[Willabe]

Yes, for fixed bias you would do that. You might have to change the value of 1 of the 2 bias resistors to get the -B voltage in the right range. But you have'nt got the bias adjustment readings right. Most guys here insert a 1R resistor between each OP tubes cathode and ground and measure across it for a reading of the tubes current. They do the same for self bias too, you just add the 1R resistor in series with the self bias resistor thats already there.    

But, I would listen to what PRR said. Go back and read his post again. If I'm understanding him right, it's not of any real benefit using fixed bias over using self bias with this tube, you want to use self bias like an AC 30. Why go through the trouble and extra exspence of self bias when you do'nt need to?


              Brad            

[Willabe]

Have you seen/read this? Very helpful!               

http://www.aikenamps.com/WhatIsBiasing.htm

http://www.aikenamps.com/Why70percent.html

http://www.aikenamps.com/Biasing.html


         Brad       

[HoodratShinobi88]

sooo a choke/big resistor 2caps and another resistor to G instead? wont I have more "control" over the amp with fixed bias, being able to adjust the negative grid voltage allows me to run "hot" and add more gain/ headroom? those pages def helped me understand it more. my moms bf is an electrical engineer when he gets back into the country im gonna ask him to elaborate on this some more. lol I feel so nubs -_-

[Willabe]

sooo a choke/big resistor 2caps and another resistor to G instead?

No. In cathode/self bias those 2 - 220K resistors get grounded at point G. They are called "grid return" resistors. Different OP tubes use different values some times.

wont I have more "control" over the amp with fixed bias, being able to adjust the negative grid voltage allows me to run "hot" and add more gain/ headroom?

Some of the guys here can explain that much better than I could.

Did you go back and re-read what PRR posted? I would follow his lead/thoughts.

my moms bf is an electrical engineer when he gets back into the country im gonna ask him to elaborate on this some more.

That sounds good.               


                   Brad