#183 questions and possible conclusions

[makrisp]

Mr. Dumble,

I am glad to see you back and I hope all is well on the home front.

[ElectronAvalanche]

Took the amp to rehearsal last night and it was overly bright in OD mode using my 4x12.

The HRM was sounding just fine over the 4x12 (Eminence Govnr + Celestion V30).

So it is back to the bench with the amp. I have a 100k trimmer pre-OD so this will be changed to 250k first.

Next will be trying different snubbers again.

@dogears:

you say anything under 150pF is questionable/hypothetical/moot. Can you elaborate a bit what you mean by that?

Cheers,

Electron

[johan]

I know some use them but I'm not fond of the V30's with Dumble-style amp. They can be very bright sounding.

[ElectronAvalanche]

I know some use them but I'm not fond of the V30's with Dumble-style amp. They can be very bright sounding.

Hi Johan,

you are right. But that is all I have at this time apart from a 1x12 EVL Dumble cab.

I used this 4x12 with the V30s with my SLO-Clone and Marshall and was quite happy.

Maybe it is time to build a 2x12 for the Dumbles.

Cheers,

Electron

[dogears]

Yeah, point of diminishing returns. The breakpoint of the HF rolloff increases as you rreduce the snubber size. You get to a point where there is little difference between them, audibly. I hypothesize that merely having something small may address tube issues above the hearing range such as oscillations. So, it may be that 25pf sounds no different than 68pf or maybe even 150pf. But, no snubbers might be different as there is no rolloff in the super highend.

@dogears:

you say anything under 150pF is questionable/hypothetical/moot. Can you elaborate a bit what you mean by that?

Cheers,

Electron

[Mr Dumble]

I know some use them but I'm not fond of the V30's with Dumble-style amp. They can be very bright sounding.

That is my experience as well. maybe the worst match of any speaker I have tried with D style amps. Just not a good match at all, although a closed back cab with them helps a bit.

[Mr Dumble]

Mr. Dumble,

I am glad to see you back and I hope all is well on the home front.

Thank you! All is well now, but my boyfrien....I mean girlfriend is moving in this weekend, so that may change soon.

[Structo]

Going by the #183 layout.

Are we positive that the Bass pot is 500K Linear?

As well as the 250K Mid pot is Linear?

And the Treble is 250K Audio?

I thought Shad had said the Treble was Linear?

Seems kind of weird.

Schematic by MRoberts shows:
Bass audio
Mid linear
Treble audio

Ford amp the whole tone stack is Audio taper.

#124 is Bass Audio, Mid Audio and Treble Linear.

[talbany]

going by the #183 layout.

Are we positive that the Bass pot is 500K Linear?

Yes...Bass Pot was unmarked and uh....it measured 311.7K ... Was a linear

As well as the 250K Mid pot is Linear?

Yes clearly labeled B

And the Treble is 250K Audio?

Yes

I thought Shad had said the Treble was Linear?

Pot is 2-35 AUD R8205- 021757

Tony

[ElectronAvalanche]

So I tried my clone last night with my 1x12 EV12L and did not find harshness at all.

Could be that the amp was not nearly set as loud as with the 4x12 during rehearsals. But I think the take home message is I need to try different speakers.

I have yet to change the pre OD Master series resistor to 180k, since the schemo I worked with showed a 100k here when it should really be a 180k.

Will report back.

Cheers,

Electron

[boldaslove6789]

Those clips do sound great. And so do clips I've heard direct from that preamp

Thanks for the kind words! Shad builds great amps!

[Structo]

Thanks Tony!

Yes I noted the 100K / 180K mistake in the Files section.

I may try the #183 preamp is why I was asking the questions.

[tubedogsmith]

another question on this amp, what was the deal with those two big resistors standing up on the power supply board? It looks like choke wires coming from under the board so.... The resistors aren't on the layout drawing either that I noticed. thanks in advance

[talbany]

another question on this amp, what was the deal with those two big resistors standing up on the power supply board? It looks like choke wires coming from under the board so.... The resistors aren't on the layout drawing either that I noticed. thanks in advance

They are balancing resistors for the plate caps...

Tony

[tubedogsmith]

Oh Ya, thanks