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Old 8th April 2008, 08:17 AM   #1
engels is offline engels  Israel
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Default Another compactron PP output

I'm planning another stupid project to recycle some of the odd parts I've got. The output tubes are 33GY7A, the power transformer is from a big solid state combo organ wreck (quite a beefy iron), the output transformer is toroid 15V with 120+120V primary. I have only one pair of tubes and one OT so this is going to be a guitar amp (mono = guitar, stereo = hi fi). Fortunately, I don't have compactron preamp tubes so I'm using some of the other semi-odd tubes I've got.

The preliminary schematics :
Click the image to open in full size.

comments welcome!
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Old 8th April 2008, 08:21 AM   #2
engels is offline engels  Israel
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Default datasheet

datasheet:

33GY7A
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Old 8th April 2008, 05:14 PM   #3
kevinkr is offline kevinkr  United States
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I'd probably use AC to heat the filaments of your 33GY7A, the half wave rectifier based filament supply you have come up with probably is not going to work too well.

I note that the filaments use 450mA so I would put them in series across the entire secondary to reduce IR losses in the windings.

I'm not too crazy about your half wave voltage doubler either, but I think that running a full wave doubler on the same winding with the filaments might be pushing your luck in terms of filament to cathode insulation ratings, but you might just squeak by..

One other thought is put the fuse before the power switch, and only switch the hot side for safety. (I am assuming you are using the standard Israeli polarized ac plug?)
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Old 8th April 2008, 05:44 PM   #4
cerrem is offline cerrem  United States
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Volume and Gain controls should be 1Meg ...else they will load down the previous stage....
The screen resistors should be inscreased...since this is for guitar...when you go into square wave clipping the output stage...the tubes will act like diodes...and you would like the screens to stay lower in potential then the plate, or else you will start arcing over ...
Is the 1K and 47uF properly decoupling??? Is the amount of attenuation to the 120Hz adequate??
Those 250V filter caps....what will the voltage be durring start-up ??? Will those caps survive start-up how many times??

Chris
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Old 20th September 2011, 10:51 PM   #5
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Default Amplifier with 33GY7A Compactron

Goodnight everyone!

This is my first post here on the site .

I always liked electronics, in particular for tube circuits (amplifiers) and decided to set up this scheme originally posted here:
Another compactron PP output

Click the image to open in full size.

My questions are:

1) Power supply: The potential drop in the use of them is of bridge rectifier 21 V it? Soon I will need a power transformer 150V, 130V for the input? The values ​​of capacitors are adequate to supply a good filter?

2) Excluding the gain and volume pots that will be exchanged for 1M, what more could be done to improve this circuit?

3) 6C4 The valve can be replaced with a 12AU7 (as I intend to build a stereo amplifier avoid using 2 6C4). There is an alternative to the valve easy to purchase 5670?

4) The dual capacitor / resistor that comes out of the cathode 33GY7A correct?
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Old 20th September 2011, 11:03 PM   #6
SY is offline SY  United States
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The 6C4 phase splitter needs to be redesigned- there's a severe error in it, it will not operate properly.
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Old 20th September 2011, 11:33 PM   #7
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Originally Posted by SY View Post
The 6C4 phase splitter needs to be redesigned- there's a severe error in it, it will not operate properly.


Aye--Like that it wont work at all!

Clue, Look at the Grid circuit....
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Old 20th September 2011, 11:42 PM   #8
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Thanks for the reply SY. What do you suggest how I could solve this problem, I do not know if the friend is asking a lot, but could put a circuit here to solve this problem?

gratefully,

Paul.
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Old 20th September 2011, 11:51 PM   #9
tinitus is offline tinitus  Europe
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as per Alastair's clue,

might it be a missing grid leak resistor from grid to midpoint of cathode and ground resistor ?

and I suppose a grid series cap is missing too ?
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Old 20th September 2011, 11:57 PM   #10
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Originally Posted by Alastair E View Post
Aye--Like that it wont work at all!

Clue, Look at the Grid circuit....

Thank you for Alastair clue, but unfortunately I do not have intimate knowledge like you to see the solution. Enlist the help of you and so learn more about tube amps.

Gratefully,

Paul
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