troubleshooting

[mat]

With nothing better to do I converted the AX84.com Hi Octane build in to ODS-101-HRM build with the Hi Octane power section with a single EL84. I know I know - no good sounds in there. Actually the amp sounds very promising but there are some things that are not right yet.

I have problem with bass pot that when turned on other side it kills the volume. Any idea where the bug might be ?

The treble is lost sometimes and when touched the PAB switch it comes back again. I swapped the PAB switch with a fresh one but the problem stays. Might be related to the first problem.

[Bob Reinhardt]

I would wonder if you are overheating the little switch for the PAB? those little switches dont take much heat at all before they have issues. I know im guilty of rendering a few of them useless

[Structo]

So I assume you have checked the bass pot to be sure it isn't defective?
Like a dead spot on the trace?

It could be blocking distortion.

Have you measured all the voltages? How do they look?

Does this happen every times you turn the bass pot up?

It sounds like the problem may be in the tone stack since you mention the bass pot and PAB.

Do you have all the values that are called for in the schematic?

What kind of phase inverter are you using before the lone EL84?

What is the EL84 biased at?

[gilgalad101]

Could it be a grounding issue with the PAB switch? Is your chassis powder coated or anodized?

[mat]

So I assume you have checked the bass pot to be sure it isn't defective?
Like a dead spot on the trace?

It gives right readings while turning the pot.

It could be blocking distortion.

Have you measured all the voltages? How do they look?

Voltages are quite low on the pre-tubes, I'll try another PT to get them up.

Does this happen every times you turn the bass pot up?

Yes it does.

It sounds like the problem may be in the tone stack since you mention the bass pot and PAB.

I'll search more on that area.

Do you have all the values that are called for in the schematic?

Only difference is that I subbed the mid pot with a 120k resistor.

What kind of phase inverter are you using before the lone EL84?

No PI. This is a single ended cathode biased amp.

What is the EL84 biased at?

I'll have to calculate that out.

I was reading from the forum that the signal should be knocked down before the EL84. Does this mean just a bigger resistor to the grid of the EL84 or something else ?

Thanks,