AC15HTTVH farty and fizzy...

[hebaton]

I can also add that running the power section in triod mode significantly reduces the problem.
Maybe this is to be expected but it seems to me the issue is with the output stage or am-I getting this all wrong

Also, it was suggested to change the C5 and C6 values ( output copling ) to .022uf I have 2000 V on hand. Would change the over all tone of the amp or just make it less sensible to strong input signlas ?

FInally, I also read about changing the phase inverter bias resister from 1K2 to 820-900
I have this ( see pic ) on hand that reads 810 ohms.

Someone please weigh in ?

This is a used amp, right? An AC15 does not have much headroom with humbucker guitars. If this is a used amp, and it has not been gone through by a tech to ensure that it is working as intended, I think it's important to rule out that what you are experiencing is either aged power tubes, tired power supply capacitors or possibly some other issue (if there is an issue..), or that it is just the voicing you don't care for.

You could certainly swap that 1k2 phase inverter tail resistor for your on-hand 810R. This could be an interesting test, because that would add more gain and a little more warmth, and bring it towards the Marshall PI voicing.

If I did swap the caps at C5 and C6 would the change how the behaves with single coils ? ( for .022uf )

[pdf64]

When I say humbuckers, I am talking 8K and 8.5 K output.

8K and 8.5K is not ouptut - it's resistance.

cheers,

Thank you. I know but, is that not how pickups are generally refered to ?

For a given magnet type and arrangement, yes, the pickup’s resistance is a general indication of its likely output level.
But those details are, as yet, unknowns here.

[ChopSauce]

If I did swap the caps at C5 and C6 would the change how the behaves with single coils ? ( for .022uf )

First it seems a bit late in the sound processing chain, second I'd be sure that the amp is operating under normal conditions before any change at all!

The circuit already seem pretty well filtered but in a few spots, maybe. By the way: how do you feel the bass shift switch behaves?

[hebaton]

If I plug in the Ef86 channel, the Bass switch seems to do it's job. There are obvious differences between positions

[JD0x0]

8K and 8.5K is not ouptut - it's resistance.

cheers,

Thank you. I know but, is that not how pickups are generally refered to ?

For a given magnet type and arrangement, yes, the pickup’s resistance is a general indication of its likely output level.
But those details are, as yet, unknowns here.

Also, don't forget about wire gauge. We generally assume 42awg, but plenty of pickups are wired with 43AWG and 44AWG or other gauges. Thinner wire has more resistance per wind but that increased resistance doesnt necessarily mean more power. Take a look at some classic tele pickups, for example. The neck is wound with 43AWG, and the bridge is wound with 42Awg, there were often tele sets where the neck pickup would have a higher resistance than the bridge, but anyone who's ever played a tele can tell the bridge is way more powerful than the neck pickups on those guitars.
An 8k pickup will have significantly different output with a Ceramic or Neodymium mag than if it was equipped with an Alnico 2 or 3 mag.

Sorry, don't mean to get off topic, but bringing this up is how we get people to stop referring to pickups by their resistance, which alone really doesnt tell you much about a pickup. 'Classic PAF' would be a much better descriptor, IMO.

Even manufactures are guilty of this. They should really list inductance spec, rather than resistance specs on their pickups, or better yet, both. Again, doesnt tell you everything about the output and sound, but it's much more helpful than a DCR reading with no other info.

[ChopSauce]

If I plug in the Ef86 channel, the Bass switch seems to do it's job. There are obvious differences between positions

For sure! I'm sorry I didn't made it more obvious: my question was more "out of curiosity", not really meant to help you troubleshoot your amp.

By the way, the switched capacitor values look a bit like "all or nothing", but the bass position doesn't seem to be your concern, right?

[hebaton]

If I plug in the Ef86 channel, the Bass switch seems to do it's job. There are obvious differences between positions

By the way, the switched capacitor values look a bit like "all or nothing", but the bass position doesn't seem to be your concern, right?

The 3 position "brilliance" switch is a bit strange. positions "off" and 1 are not very different rom earch other but position 2 seems to cut out most of the bass.
But to answer your question, part of my concern is with the bass response that becomes rapidly overwhelming making it fifficult to dial in a good tone with humbuckers. Headroom is also an issue with those.
I am thinking of installing some sort of Master volluin there .