What to tweak?

[Tdale]

Is it possible to make a list of which components that are most important in the tweaking process?

Let's say I have a basic amp, with the "normal" way of doing things. What components are the ones that change sound the most?

Coupling caps? Components in the tone stack?

What about plate resistors or cathode resistors/caps?

Where do you guys do your tweaking?

Also, I find the OD entrance kind of interesting. There are so many ways to do this it seems, either the 200K into the 100K pot, or a bridge resistor with a couple of resistors to ground from each side.. some have a trim pot, some don't.. Is this a part of the amp where tweaking makes a big difference?

[Bob-I]

Cathode bypass caps are a biggie, tone stack caps and pots, snubber caps, series resistors and coupling caps.

Tubes make a big difference as does bias.

Where's dogears when you really need him......

Ok, truth, Scott's alway there when you need him as is Gary.

[Tdale]

If I want to change the value of the cathode bypass cap, do I need to change the plate resistor too, or doesn't that matter as long as the changes are small?

Tommy

[dogears]

I believe you are confusing the cathode resistor with the bypass cap. If you change the cathode resistor, you should change the plate resistor to the appropriate scaled size (if you are keeping the RCA 67:1 ratio). However, some Dumbles have mismatched sets for specific tonal purposes. Experimenting may be what you want to do...

Typically when changing the bypass caps, you are just tuning the high pass shelving filter. Or, in other words, just trimming bass.

Bob is correct IMO. Tweaking the preOD network, coupling sizes, snubbers, component types, tone stack values, filter cap size, interstage series resistors, voltage levels, bright cap on master, choke or no choke, etc.... All yield noticeable changes. You need to try these things out so you know in your head the general effects of each type of tweak. It greatly helps tuning in the future....

If I want to change the value of the cathode bypass cap, do I need to change the plate resistor too, or doesn't that matter as long as the changes are small?

Tommy

[Bob-I]

Bob is correct IMO.

Steal from the best, that's my motto.

[groovtubin]

I believe you are confusing the cathode resistor with the bypass cap. If you change the cathode resistor, you should change the plate resistor to the appropriate scaled size (if you are keeping the RCA 67:1 ratio). However, some Dumbles have mismatched sets for specific tonal purposes. Experimenting may be what you want to do...

Typically when changing the bypass caps, you are just tuning the high pass shelving filter. Or, in other words, just trimming bass.

Bob is correct IMO. Tweaking the preOD network, coupling sizes, snubbers, component types, tone stack values, filter cap size, interstage series resistors, voltage levels, bright cap on master, choke or no choke, etc.... All yield noticeable changes. You need to try these things out so you know in your head the general effects of each type of tweak. It greatly helps tuning in the future....

If I want to change the value of the cathode bypass cap, do I need to change the plate resistor too, or doesn't that matter as long as the changes are small?

Tommy

Dogears, wondering if the DEGOOPED pix have helped you in your tweaking adventure? I`ve thrown out the book, it seems to help me alot! LOL! jim

[dogears]

Hi Jim,

The pics only helped since they are radically different than Hybrid A. That dispelled the myth that the Hybrid A is the end all circuit. Like you said, it threw out the book. Having said that, I do think a variation on Hybrid A is a great sounding amp......

It also reaffirmed my belief that the quality of plate resistor is important

I believe you are confusing the cathode resistor with the bypass cap. If you change the cathode resistor, you should change the plate resistor to the appropriate scaled size (if you are keeping the RCA 67:1 ratio). However, some Dumbles have mismatched sets for specific tonal purposes. Experimenting may be what you want to do...

Typically when changing the bypass caps, you are just tuning the high pass shelving filter. Or, in other words, just trimming bass.

Bob is correct IMO. Tweaking the preOD network, coupling sizes, snubbers, component types, tone stack values, filter cap size, interstage series resistors, voltage levels, bright cap on master, choke or no choke, etc.... All yield noticeable changes. You need to try these things out so you know in your head the general effects of each type of tweak. It greatly helps tuning in the future....

If I want to change the value of the cathode bypass cap, do I need to change the plate resistor too, or doesn't that matter as long as the changes are small?

Tommy

Dogears, wondering if the DEGOOPED pix have helped you in your tweaking adventure? I`ve thrown out the book, it seems to help me alot! LOL! jim

[groovtubin]

Hi Jim,

The pics only helped since they are radically different than Hybrid A. That dispelled the myth that the Hybrid A is the end all circuit. Like you said, it threw out the book. Having said that, I do think a variation on Hybrid A is a great sounding amp......

It also reaffirmed my belief that the quality of plate resistor is important

I believe you are confusing the cathode resistor with the bypass cap. If you change the cathode resistor, you should change the plate resistor to the appropriate scaled size (if you are keeping the RCA 67:1 ratio). However, some Dumbles have mismatched sets for specific tonal purposes. Experimenting may be what you want to do...

Typically when changing the bypass caps, you are just tuning the high pass shelving filter. Or, in other words, just trimming bass.

Bob is correct IMO. Tweaking the preOD network, coupling sizes, snubbers, component types, tone stack values, filter cap size, interstage series resistors, voltage levels, bright cap on master, choke or no choke, etc.... All yield noticeable changes. You need to try these things out so you know in your head the general effects of each type of tweak. It greatly helps tuning in the future....

[dogears]

Jim,

Interesting observation since everytime I try CC or CF on Dumble circuits the sound goes big time bye bye!!! Metal film it is for me.....

[groovtubin]

Jim,

Interesting observation since everytime I try CC or CF on Dumble circuits the sound goes big time bye bye!!! Metal film it is for me.....

[BobW]

Groovtubin and Dogears, those are interesting obervations. The CCs have practically zero inductance, (not including the leads), which is why they are used a lot in RF circuits. In the past I've used CCs as the plate and cathode resistors but found over time the high value plate resistors became noisy and popped, as also mentioned in the trainwreck notes and elsewhere on the web. Am using MF resistors on my 50W and am overall satisified, however, have never A/B'd the difference in MFs vs. CCs or CFs.
I am using cheap sand filled 5W for the screens, but am curious to know you opinions. The noise factor seems acceptable.

Dogears your suggestion to change to CER caps for the lower pf values made the most significant difference in tone, in the positive direction! Was previously using silver micas. Who ever would have guessed the cheaper, the better?

[Tdale]

Snubbers are caps that go across a resistor or diode, right? What snubbers are you talking about when it comes to tweaking?

Tommy

[llemtt]

..wondering if the DEGOOPED pix..

Hi Jim

Do you really mean DEGOOPED instead of NOTGOOPED?

I never saw a DEGOOPED Dumble, Have you? Is it so different?

Teo

[mlp-mx6]

Snubbers are caps that go across a resistor or diode, right? What snubbers are you talking about when it comes to tweaking?

Tommy

What we commonly call "snubbers" around here are the pF-sized caps that go from plate to cathode on the two OD triodes.

[dogears]

Hi Teo,

Degooped is what happens when you spend months meticulously picking away at the goop. When it is really clean, you then take a bunch of really nice photos.

I can't share them here, but I can say that the grail sounding speciman had 25uf caps on V1a and V1b. .05/.01/.005 couplers. And importantly, the skyliner stack in combination with no post OD stack. Nice plates that looked like Vishay Dale RN65s and PS series OD caps.

There are other degooped ones as well. Interesting stuff that is not in the never been gooped ones.

..wondering if the DEGOOPED pix..

Hi Jim

Do you really mean DEGOOPED instead of NOTGOOPED?

I never saw a DEGOOPED Dumble, Have you? Is it so different?

Teo