1/2 watt guitar tube amp single 6AQ5 12AX7 No harmonic overtones.

[streamz1]

I got this amp on ebay. Gain stops just before harmonic overtones, sustain want to kick in. I'm wondering if it's a plate voltage issue or otherwise. Any advice would be appreciated. I'm aso using 75 watt 2x12 cab.

Unbalanced line out provides level for recording or playing out through a mixer.
Will drive DI (direct) box to go from unbalanced to balanced for long runs. Will also
act as a preamp to drive larger power amps with a line input.

Includes a switched speaker load (10ohms) when using as a preamp if you desire not to
drive a speaker at the same time.

It is a single ended 6AQ5 (Jan6005) output tube biased into saturation and driven by a 12AX7 (ECC83) tube as a two stage preamp.

The first stage is a switchable tube/jfet cascode preamp allowing a gain of 30 or 100 for cleaner tones or much more overdrive.

The guitar signal passes through both gain stages to provide nice, preamp overdrive.

The gain pot is is in the middle to adjust the amount of overdrive. The output of the preamp feeds the master volume control.

The volume then drives the single ended output stage for a full range of output level.

Will work fine with you favorite sealed, ported, or open back, 4, 8 or 16ohm cabinet, preferably with 6 inch or greater speaker(s).

[diagrammatiks]

yikes don't shake that guy too hard.

Try hitting in front with a boost?

gah why are the preamp tubes biased like that. that's just stupid.

you barely have any signal swing and it's unbypassed too so you barely have any gain.

no wonder you can't drive the power tube.

[streamz1]

Put a tubescreamer in front, better not the same. looking for simple mod. if possible.

[streamz1]

yikes don't shake that guy too hard.

Try hitting in front with a boost?

gah why are the preamp tubes biased like that. that's just stupid.

you barely have any signal swing and it's unbypassed too so you barely have any gain.

no wonder you can't drive the power tube.

Put clean boost in front full throttle, louder, started to get overtones, but not thier yet.

[streamz1]

The Fix
1 22 microfarad / 35 volt + to pin 3 of the 12ax7 and - to ground.
1 22 microfarad / 35 volt + to pin 2 of the 6AQ5 and - to ground

[J M Fahey]

Those triodes look too hot biased for my taste; what DC voltage you got on those plates?
What's wrong with classic 1K5//10uF?
I don't get you: you speak of "nice, preamp overdrive. ".
*If* you overdrive that second triode, it's output signal should *nuke* that poor 6AQ5.
Even more if you bypassed that 270 ohm cathode resistor.
On whose value I'm not quite sure either; I'd check 6AQ5 datasheet and use whatever they suggest.
Nice recycling of a computer PSU case.

[loudthud]

B+ is only about 160V. Maybe a voltage doubler would improve things.