Is a 50v Presence cap too small for 100 watt amp

[rootz]

I’d guess 100k log pots for reverb send and return?

Any clue what that 10meg resistor is doing over there a the grid of v3b?

Another guess: trimmer and cap shunt high end to ground in the tone stack when PAB is engaged.

[Guy77]

I’d guess 100k log pots for reverb send and return?

Any clue what that 10meg resistor is doing over there a the grid of v3b?

Another guess: trimmer and cap shunt high end to ground in the tone stack when PAB is engaged.

Hi Bas. yes the Reverb Send and Return are both 100k pots! The slope resistor in the tone stack it is not 150K it is actually 100K slope resistor!

I attached the connections for the PAB relay. I didn't draw it but yes the PAB switch is connected to the PAB relay just like in all the original Dumbles.
The 1M trimmer on the relay board is one of those that has the middle wiper as 2 arms that are on each side of trimmer. The other 2 arms are the far left and far right arms like on all standard trimmers.
Hopefully my old tech drawing and your high tech skills can equal a schematic. thank you Bas!

All the resistors on the OD tube (V4) are the same as on all the standard #124 ODS except this has no snubbers. I think snubbers would smooth out this Overdrive and make it sound better.

Also every cathode resistor and cap in this amp is 1.5K/4.7uf 100v except for V3a which is 1.5k/10uf 100v.
Also resistor feeding reverb tube (V2a) from v1b is 68k.

Phase inverter plate resistors are 110k and 120k.
Both OD plate caps for v4a and v4b on the board are .01uf

The power tube plates are running at about 436V with 120v wall voltage. This power transformer has about the same weight as the Hammond Twin reverb replacement and the same B+ voltages.

PABrelay.jpeg

BloomDrive.jpg

[talbany]

The overdrive sounded a little thin and the owner wants them a little fatter.

I am thinking about possibly building one of these If I did a few things I would do?

1.Add the snubbers
2.increase the value of the OD entrance trimmer. (like 124) and or increase the value of the OD Drive to 250k (linear taper)
3.100/110k on PI
4. Build it with AB Carbons instead of the Speers.

That should help fatten up the OD. Since you say the clean channel already sounds good w/ 5uF.I would start there as long as everything else being as per 124 values.

Tony

[dimitris]

Thanks for all that information Guy.
I would expect the trimmer/capacitor on the pab board to be connected to the treble pot only when the pab would be engaged.

[rootz]

Thanks again Gaetano for checking all the stuff we asked!

I do believe the 10uF bypass cap should be on V3b's cathode, or am I seeing this wrong in the pictures? Probably there just because 4u7 was not available/within reach. The other Bloomfield drive I've seen, had 4u7 through the whole amp.

Anyway, here is the schematic. I left out the 2n2 on the reverb return RCA. And I must say, my first schematic came pretty close (pat myself on the back )! Can you spot any obvious mistakes?

[Guy77]

Thanks again Gaetano for checking all the stuff we asked!

I do believe the 10uF bypass cap should be on V3b's cathode, or am I seeing this wrong in the pictures? Probably there just because 4u7 was not available/within reach. The other Bloomfield drive I've seen, had 4u7 through the whole amp.

Anyway, here is the schematic. I left out the 2n2 on the reverb return RCA. And I must say, my first schematic came pretty close (pat myself on the back )! Can you spot any obvious mistakes?

Hi Bas! You did that faster than it took me to draw my pictures, nice! Thank you Bas.
Everything looks great except the bright cap is 180p on the Bloomfield. and the phase inverter plate resistors are 110k and 120k although I prefer what you wrote instead.

Great job Bas!!!!!!

Thanks for mentioning how the PAB trimmer works Dimetris.

Tony, you will like the silky clean tones of this amp, lots of sparkle, it has has great sustain too.

[talbany]

rootz
You da Man!.. A few things at a glance.. Mixing resistor is 270k not 220
The original has no snubbers not sure if you added those in or?
also I see you label your pots differently with a letter and a number. i am old skool so is that some kind of number system or is there a legend attached?

Great work!

Tony

Tony, you will like the silky clean tones of this amp, lots of sparkle , it has has great sustain too .

I don't doubt it thats why you shouldn't touch the clean side and try to tweak just the OD.
So a question on the reverb is how does it sound while in OD. Is it weak or boomy have a long delay and is it mixed in well? (trail the note or surround it). I want just enough to give the amp depth not a surfer

Thanks!

[rootz]

Guy, can you make some more pictures? I'd like at least one showing the complete guts, zoomed in a little and perfectly perpendicular to the top side of the chassis (off course photographing the inside/components. With all sides straight (photoshop for perfection), I can make a accurate layout of the amp, if folks here would like that.

[rootz]

Oh crap, forgot to change the resistor to 270k.
I added those snubbers just for you Tony
Pots are always a letter and number combo in LTSpice. There is no logic there to help us. Not needed either, we know which pot does what.

Like Tony, I'm also curious how the reverb sounds while in OD. This is clean reverb mixed in with dry OD! I can't hink of any other amp doing that. It's not a Dumble thing either AFAIK. Maybe ODRS #59 does this also? #60 most certainly doesn't.

Oh and Tony, if you're into good sounding Two Rocks: the Custom Reverb Signature V3 is one too!

Now that PAB relay still makes me wonder what the point of the trimmer/1n combo is. It is permanently connected to the bass pot middle lug. It does seem to shave of high end and some (lower) mids, but especially when PAB is engaged. Anyone ever tried such circuit?

[mojotom]

Now that PAB relay still makes me wonder what the point of the trimmer/1n combo is. It is permanently connected to the bass pot middle lug. It does seem to shave of high end and some (lower) mids, but especially when PAB is engaged. Anyone ever tried such circuit?

Drawn as you schem I see it connected to the treble pot lug going to the PAB. It should shave some highs. Why more on PAB ? Looks like an always ON treble bleed to me (but I checked briefly).

It reminds me of Brownface tonestack with a 70k taper on the treble pot connected to ground via a cap.

His first ODR and ODSR amps were pre OD reverb. Don’t know how much but I guess maybe more build like that rather the post OD (number of ODSR amps). Some could have been modded to post later on (maybe 59, probably 60).
Only tried Post OD amps, don’t know what to expect from a Pre OD.

[Guy77]

rootz
You da Man!.. A few things at a glance.. Mixing resistor is 270k not 220
The original has no snubbers not sure if you added those in or?
also I see you label your pots differently with a letter and a number. i am old skool so is that some kind of number system or is there a legend attached?

Great work!

Tony

Tony, you will like the silky clean tones of this amp, lots of sparkle , it has has great sustain too .

I don't doubt it thats why you shouldn't touch the clean side and try to tweak just the OD.
So a question on the reverb is how does it sound while in OD. Is it weak or boomy have a long delay and is it mixed in well? (trail the note or surround it). I want just enough to give the amp depth not a surfer

Thanks!

Guys I take back what I said about the OD sounding too edgy and thin. Its because I hade the OD Volume down too low! I had it turned down to like 7:30am on the dial as soon as I took it into the garage and opened it up half a notch to 8 or 8.5 or 9 am on the dial it became a lot fuller sounding! I now really like the overdrive on this amp but I may still add snubbers.

The reverb actually sounds just fine when in Overdrive, it does not get too boomy when turned up and adds a nice ambience to the Overdrive sound if just turned up a bit. The reverb can get fairly intense when cranked but not like a fender does. I was not expecting post OD Reverb to sound this good!

I did an A B test with my own Post ODS Reverb amp and they sounded very similar! Only time a gave a slight edge to my Post Overdrive Reverb was if I cranked my Reverb Return to 3pm on both amps ( I had the Send knob cranked all the time) and then I gave a slight edge to my Post OD reverb for mixing with more clarity. So if your one that doesn't crank the reverb it sounds great.

This sounds like a Medium decay Reverb just like in my Post ODS Reverb amp. The tank bag is closed up tighter than a kangaroos pouch LOL. I will try to open it in a few days. Cleans are heavenly.
One other thing about this reverb that I like is that it does not add any treble or any bass to the sound of the amp as you turn it up. I like this a lot.

I will have to build this amp. The cleans are the bomb

Oh yes mixing resistor is definitely a 270K

EDIT: I will adjust the PAB trimmer while playing and let you know how much it effects the tone while PAB is turned off/on.

Here is top pic you asked for Bas,

Guy

20210609_200527 - Copy.jpg

20210609_200523.jpg

[talbany]

Thanks guys for the rundown on the reverb's performance. I was a little worried that only a 1/2 stage gain might be a little light on the current to drive the tank. Doesn't sound like it.
I played a Custom clean years ago but didn't have enough time to put it through it's paces and really crank it but remember it sounded pretty good and quite a few friends of mine have nothing but good things to say about it. For me I personally like a little reverb on the clean side it's the OD I generally have an issue with the spring reverb clogging things up. I wonder how this does compared to the one set up in the CC. Any opinions or recommendations schematics are welcome.

Guy. Generally I too have found that the low plates can sound a bit thin until you pour the coals to it.
Thanks again rootz/Guy for the amp & schematic and yes I think a layout would be wonderful!!

The Amp Garage strikes again!

Tony

[rootz]

Guy, just on more pictures request: please the full chassis in just one shot. So like you did the last two pictures, but all in one shot. The complete chassis has to be visible.

[rootz]

Tom, you are right. Trimmer/cap connected to bottom of treble pot. But also to bass wiper and top if PAB is off and in rock mode.

Sims confirm it has little effect in rock mode with PAB off, only when going low on the trimmer it starts to work then. Say the last 100k (I’d say when approaching brownface values).

It’s effect is not only on the high end. There seems to be even more effect on the (lower) mids. Shaves of 5 to 6 dB around 200/300 Hz and around 3dB at 10kHz.

This amp is also not pre od reverb like #13 we all know. That one has the complete reverb section mixed in before the od relay. Here the reverb is taken from the cleans, but mixed back after the od relay. So, to me, this looks like a a crossover between pre and post od reverb.

Also, the mixing of the reverb is set/influenced by the 270k mixing resistor and the output impedance of either the last clean or od triode/stage. Those are your build in mixing resistors so to speak. Again significantly different from #13 and #60.

[rootz]

Tony, I have build a straight clone of the TR custom reverb signature V3 (the AN Wonderland Overdrive v1 was utilised the same topology). This amp is post master volume reverb (so also post od) with a single 12ax7 triode driver and gets very strong reverb that way. Why? Because of a strong recovery stage and tweed mixer. So the signal going through the tank might be small, there is enough amplification after the tank to make up for that.

Now in another build I made almost the same reverb, but moved it in front of the master volume and used a 12at7 as driver and first recovery stage. Now that has some serious reverb! But also well behaved and controlled due to local feedback loops on driver and recovery stages. In Dumble fashion.

Sounds like the concept of a TR Coral is something you’d really like. That amp has dual reverb send and return controls, so separate for cleans and OD. This is extremely versatile imho.