high octane push pull??
Moderators: pompeiisneaks, Colossal
high octane push pull??
A guy gave me this circuit board. he thought it was a Trainwreck (its not), then thought maybe it was an AX84. the preamp looks similar but its got 2 power tubes (6BQ5/EL84). I got the board and a diagram of the lay out. the board is already built and looks pretty well done. I've checked the components and they match the diagram except for a couple numbers that I'm not sure of because the print is not too good. I've been to AX site but there is nothing about this one. other searches I've done are dead ends, the old sites are gone or infected, etc. anyway... what I want is the schematic. or at least the transformer specs. and the pots, especially the ganged GAIN pot. the others I can prolly guess
Re: high octane push pull??
The guys at ax84.com were known to experiment quite a bit with amps, especially mix and match preamps and power amps.
The preamp circuit is the same as the hi octane preamp, but a few component values are different. So, use the hi octane schematic for everything between the input jack and the (master) volume wiper.
The phase inverter and power amp are the same as a Marshall 1974 (18-watt) amp, but a few component values are different. So, use the 18-watt schematic for everything between the PI input and speaker jack.
The dual gain pot is two 500K-A pots. It's impossible to know from your drawing if the shafts are ganged or dual concentric. For maximum flexibility I suggest using two separate pots or dual concentric.
I would use readily available iron for a Marshall 18-watt amp.
I was able to read all the component values on your layout. Which ones were you unable to read?
The preamp circuit is the same as the hi octane preamp, but a few component values are different. So, use the hi octane schematic for everything between the input jack and the (master) volume wiper.
The phase inverter and power amp are the same as a Marshall 1974 (18-watt) amp, but a few component values are different. So, use the 18-watt schematic for everything between the PI input and speaker jack.
The dual gain pot is two 500K-A pots. It's impossible to know from your drawing if the shafts are ganged or dual concentric. For maximum flexibility I suggest using two separate pots or dual concentric.
I would use readily available iron for a Marshall 18-watt amp.
I was able to read all the component values on your layout. Which ones were you unable to read?
Re: high octane push pull??
on the far left of the boaed... is that 2.7k? thats the one I'm not sure of. and the grid resistors. thanks!
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sluckey
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Re: high octane push pull??
I spliced the Hi-Octane preamp to the 18 Watt power amp. The red component values are what show on your layout. I also fixed some errors on your layout and separated the ground buss to have a power ground and separate preamp ground. And I did away with the series 100µF reservoir caps and replaced with a single 50µF and 220K bleeder resistor.
Yes, 2K7. Grid resistors on the sockets are 5K6.on the far left of the boaed... is that 2.7k? thats the one I'm not sure of. and the grid resistors. thanks!
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Re: high octane push pull??
OK, thanks! I have a Hammond 290PAZ on the shelf... that should do for the PT right? I also have a Hammond 1620 OT... what do you think of that? 20W and 6k6 input impedance
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Mac Dillard
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Re: high octane push pull??
Not meaning to hijack thread, but a question, if this build is to bright, would deleting c13 be a good place to start increasing bass. Tks
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sluckey
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Re: high octane push pull??
290PAZ is great. If I had a 1620, I'd use it, but if I had to buy, I'd get the 1750PA.