Is 33k the "standard" value for V1a for 100k plate

[Charlie Wilson]

Hello, I have been looking at all of the photos of 100k plate amps I have both skyliner and classic and notice that that all have a 33k v1a grid resistor. This includes #124,Borderline, and the Carlos Rios amp. I am wondering if anyone who has been inside real Dumbles has ever seen a 100k amp with a 22k V1a resistor. I ask this because I have a Low Plate Classic circuit and for awhile I had the 33k and it seemed to sound good. However after finding and correcting a few issues with my amp that were corrupting my tone and feeling confident that it is 100% I felt that my tone was pretty midrange focused and lacked some of the high end chime with my strat. I recently went back to the 22k and I was surprised at the difference. Not only did I get all of the nice high end stuff but the bass was better also. I know it has been said that the difference between the 22k and 33k is slight. In my amp, it made a big difference and I much prefer the 22k.
CW

[ToneMerc]

https://www.ampbooks.com/mobile/amplifi ... d-stopper/

TM

[Charlie Wilson]

Thanks Mike. Playing around with that calculator the difference looks way more subtle than what I am hearing. I think I should probably also read the book that is referenced.
CW

[UltraHookedOnPhonix]

Total capacitance for input triode is about 150pF.

With a 33K grid resistor, you're looking at about 32kHz roll-off with a -6dB/octave slope.

With a 22K grid resistor, it's around 48kHz.

Both values do a nice job of reducing incoming RF interference.

Here's some great info on miller capacitance:

http://www.aikenamps.com/index.php/what ... apacitance

http://www.valvewizard.co.uk/gridstopper.html

[marcos]

Charlie,
FWIW, my personal amp (1979 50 Watt ODS) has 22k as the V1a grid stopper.
I have experimented with this value on other amps, I especially remember
changing this resistor on a PRS Sweet 16, which had 50k there, and I was amazed at the difference in tone when changing to smaller values.
I feel that it does a lot more in terms of tone than you would
expect after calculating the frequency roll-off.
One more surprise, hope this is helpful,
BTW I really appreciate your contributions

Marcos

[Max]

I am wondering if anyone who has been inside real Dumbles has ever seen a 100k amp with a 22k V1a resistor.

Here's a picture. Source: http://personalpages.manchester.ac.uk/s ... 20%230040/

Cheers,

Max

[Structo]

Seems most his amps have the 22K grid stopper.

I believe #124 has a 33K resistor.

That's what I put in mine.

[ayan]

That has not been my observation. Most if not all non HRM amps have a 33K V1A grid stopper. HRMs, Blues Masters, etc., seem to use 22K.

Gil

Seems most his amps have the 22K grid stopper.

I believe #124 has a 33K resistor.

That's what I put in mine.

[norburybrook]

maybe that's a small part of the reason the BM has a more fendery/brighter clean channel than the #102.


Marcus

[Charlie Wilson]

Thanks guys. Max, thanks for the photo. I guess I should have been specific about the generation I was curious about. I was thinking more the 4th generation classic and skyliner amps. What got me thinking about this was Tony's layout which I followed, has 22k as the grid resistor yet #124 has a 33k. The other thing is these 4th generation amps seemed mostly to have RG59 coaxial(originally) that is about 16pf per foot, so they probably are pretty bright. That along with 100k plate resistors might have made the 33k grid resistor not attenuate the highs quite as much. In my amp I have coaxial that is about 30pf per foot so the 33k kills all of the nice high end stuff with my strat. Gil, attached are a couple of high plate classic photos with 22k although that may not have been the norm.
CW

[Max]

I was thinking more the 4th generation classic and skyliner amps.

The picture of this value (22k) in #0040 is just an example for "non-HRM". I remember having seen this value (22k) in original ODS amps with a "classic" tone stack and a "standard" OD circuit (trigger entrance, ratio pot, snubbers) in transition generation and 4th generation chassis, and in original ODS amps with a "skyline" tone stack and a "standard" OD circuit in 5th generation chassis, too. As an example I've attached a layout of an ODS 100W with a "skyline" tone stack and a "standard" OD circuit in a 5th generation chassis. Source: http://ampgarage.com/forum/download/file.php?id=16846

BTW: These are Dumble amps. So IMO based on my personal experiences there isn't something like "the norm" - even in regard to ODS amps with very close serial numbers built into the same kind (generation) of chassis (let alone SSSs or DLs etc.).

Cheers,

Max

[Charlie Wilson]

Thanks again Max. I guess my inquiry was specifically about 100k plate load amps and the possibility that Dumble used the higher 33k value as a way of taming the brightness. Being the flip flopper that I am, I tried the lower 5uf bypass caps on the clean side and then tried the 33k again and now I like it. In my amp, there was something about the 10uf caps that was making my high end a little harsh. I then lowered the V1b coupling cap to .02uf and now my amp sounds really good with Strats and other Fender guitars. Not as good on the clean with humbucking guitars. I guess it is my version of the Carlos Rios amp without the mid boost. I also tried the lower 3k3(or so)/270ohm NFB values but didn't like it. It dulled the amp too much for my taste.
CW

[Structo]

I'm not sure I am correct but it seems the HRM, Bluesmaster, and later El34 amps were sometimes described
as more 'Marshally' with a brighter tone than the Skyline, High Plate amps with the 6L6's. (#102, etc)
Maybe that was the reason he chose a 22K Rg.
It would make sense since those amps seem to have a brighter bite (to me at least from recordings)
than more common ODS amps.


PS
Thanks for the nice photos Charlie!

[Structo]

The guy that makes amps in Malaysia uses 47K on his HRM.

[David Root]

I have seen somewhere, and I think most likely here on TAG, that he used 22k for players with a light touch and 33k for those with a heavier playing style. Regardless of the circuit. That would account for the inconsistencies between ODS types.

Extending that ad absurdum, SRV's amps would have used maybe 100k!