Master volume for Tweed deluxe

[Leevi]

This subject has probably been handled here earlier but I ask anyway.
Is there a working/proven solution for a 5E3 master volume?

/Leevi

[kagliostro]

Hi Leevi

http://www.el34world.com/Forum/index.php?topic=10243.0

Kagliostro

[Leevi]

Thanks Kagliostro for your response.

I have drawn the following power amp based on 5E3 and would like to get
comments regarding the PPIMV in the picture. Do you think it would work as it has
been drawn?

/Leevi

[sluckey]

That'll work. I'd probably use 500K pots and replace the 2.2megs with 470Ks.

[kagliostro]

Hi Leevi

Yes I think it will work

you can also try this

http://www.el34world.com/Forum/index.php?action=dlattach;topic=10243.0;attach=19862

Kagliostro

p.s.: I think that the two resistors, between the wiper of the pots and ground, in your cathode bias amp aren't necessary, if I'm not wrong their purpose is to avoid problems in fixed bias amps if the wiper disconnects

[Leevi]

p.s.: I think that the two resistors, between the wiper of the pots and ground, in your cathode bias amp aren't necessary

Yes I was wondering the same thing. I have originally got this setup from some forum related to XITS amp.
Maybe it scales the control somehow?

I'd probably use 500K pots and replace the 2.2megs with 470Ks

Sluckey, what is your idea in this?

/Leevi

[sluckey]

The 2.2meg are used to keep the grid biased (either negative bias voltage for fixed bias amps or ground return for cathode biased amps) in the event that the pot wiper fails open. It's a good idea. But 2.2meg 'may' be more grid resistance than a 6V6 would like to see.

My idea of using 500K pots and 470k resistors will still give the original grid resistor value of 220K (or close enough). Now if the pot fails, the grid resistance only goes up to 470K which is fine for the 6V6.

That's just the way I'd do it. Your values works fine too.

[Leevi]

Ok, thanks. I suppose linear pots would work better in this?
/Leevi

[sluckey]

I would use audio taper for the same reason to use audio taper for most all volume controls.

[FYL]

Is there a working/proven solution for a 5E3 master volume?

My fave is the bootstrapped PI MV, KOC-style. Transparent at all settings, low parts count, just what the doctor ordered.

[Leevi]

Looks quite simple FYL. Have you tried it? Are there any drawbacks?
/Leevi

[FYL]

Looks quite simple FYL. Have you tried it? Are there any drawbacks?

Very simple, very effective. It's my standard MV for concertina-based power amps. No drawbacks. Some have reported a form of signal leakage at very low settings diminishing it's effectiveness but it's IMO a wiring/routing problem in their builds.

You may also play with the 10K grid R. Using a 220K or 330K - Merlin B. advocates up to 1M - cuts nasty blocking disto when the amp is overdriven.

[kagliostro]

OK Sluckey thanks to explain the use of those resistors, I was wrong thinking they will be only for fixed bias

FYL the difference of your bootstrapped PI MV compared to a standard PI MV is that the pot reach the ground crossing the resistor instead of directly

can you or someone explain which is in detail the difference in function ?

Thanks

Kagliostro

[TIMBO]

Hi guys, Got PPIMV on my last build and so far no problems.  

[phsyconoodler]

FYL,

Can you show your master version in a layout? I am having trouble seeing it as it is(just me and schematics)

[FYL]

compared to a standard PI MV is that the pot reach the ground crossing the resistor instead of directly

can you or someone explain which is in detail the difference in function ?

A typical PPIMV is a resistive attenuator in series, with bandwidth and tone depending on RC time constants. Some work very well, others are unusable.

A bootstrapped MV wraps a stage and creates a local positive feedback loop. RC time constants are fairly constant for all settings, even if the R portion is seen reflected at many times it's actual value.

In the Concertina the MV stands atop the bottom bias resistor, keeping bias current nearly constant for all settings.

[sluckey]

Can you show your master version in a layout? I am having trouble seeing it as it is(just me and schematics)

Here you go. This is my 5E3 layout with that exact MV.

[DummyLoad]

hey steve, couple of questions... have you had any oscillation tendencies with the 1st stage grid-leaks (68Ks) on the ckt. board, and have you built the 5E3 with FYLs concertina MV, or did you just post the dwg. to help mr. phsyconoodler?

much thanks,

--DL

[sluckey]

I've not had any oscillation problems with the 68Ks on board. I also have never really pushed this amp. Been in the bedroom since I built it. The layout is similar to the original. I don't have the MV on my amp. I just drew that for phsyco. Bet he likes the schematic better now!   

[DummyLoad]

I've not had any oscillation problems with the 68Ks on board.

thanks, good to know... on the breadboard, i can't tell if one method is better than another. with the high gain stuff i prototype, experience has shown that lead-dress is by far more critical.

Bet he likes the schematic better now!   

 

did you really use 1W CC for the plate loads? seems like overkill, unless you have a large stash of 100K and 56K 1W CC which no one still seem to want.

peace.

--DL 

[sluckey]

did you really use 1W CC for the plate loads? seems like overkill, unless you have a large stash of 100K and 56K 1W CC which no one still seem to want.

I did. Somewhere along the line I heard they were less noisy than 1/2 watters. I don't know if that's true though. And I really used 2 watters on the power rail. I have access to a large stash of 1/8, 1/4, 1/2, 1, and 2 watt CCs. Most sizes have a complete value range from 1 ohm to 10meg, including numbers that you likely never saw in a local tv shop, ie, 11x, 16x, 20x, 24x, 30x, 36x, 43x, 51x, 75x, 91x. They've been in bench stock for over 30 years, so I have to check'em befor I use'em.

[DummyLoad]

they would be a bit less noisy. don't think you could tell though.

nice compliment of power tubes.

i tried the bootstrapped concertina MV on my breadboard last night. indeed, it is very transparent. i use a 680K-1M for the grid-leak. the 1M starts shaving off highs noticeably. 820K is fine. i did revert to the 1M grid-leak since the amp i am bread-boarding is bright.

peace,

--DL

[Leevi]

I'm currently building a 5E3 with MV and would like hear more technical pros/cons which one the
proposed MVs I should select: bootstrapped concertina MV or PPIMV?

/Leevi

[DummyLoad]

bootstrapped concertina gets my vote. but then again i build weird stuff, so take my advice accordingly...   

peace.

--DL

[kagliostro]

A typical PPIMV is a resistive attenuator in series, with bandwidth and tone depending on RC time constants. Some work very well, others are unusable.

A bootstrapped MV wraps a stage and creates a local positive feedback loop. RC time constants are fairly constant for all settings, even if the R portion is seen reflected at many times it's actual value.

In the Concertina the MV stands atop the bottom bias resistor, keeping bias current nearly constant for all settings.

Many thanks FYL

Sluckey your amp has a fantastic layout ! 

Kagliostro

[skeezbo]

Has anyone tried the crossline master volume on an amp with a cathodyne inverter? That one seems very simple, too, as far as the parts count, but no one has mentioned it.  No good?

Skeez 

[tubenit]

Yes, I have done the crossline master volume with an on/off 1M pot. It doesn't sound very good at all, IMO. I almost never turned it on.

With respect, Tubenit

[FYL]

Has anyone tried the crossline master volume on an amp with a cathodyne inverter? That one seems very simple, too, as far as the parts count, but no one has mentioned it.  No good?

The crossline shows a very limited useful range with a huge loss of transparency/brillance at low to mid settings. Not very useful IMO, except in some overly bright EL84-based amps.

[Fresh_Start]

Has anyone tried the crossline master volume on an amp with a cathodyne inverter? That one seems very simple, too, as far as the parts count, but no one has mentioned it.  No good?

The crossline shows a very limited useful range with a huge loss of transparency/brillance at low to mid settings. Not very useful IMO, except in some overly bright EL84-based amps.

I had similar, poor results trying a crossline PPIMV in a Princeton Reverb.

Cheers,

Chip

[sluckey]

Poor results here also. My Matchless Lightning clone has a crossline MV and I find it almost useless in the bedroom. It may be more useful in a clube environment though. The lightning uses a LTP PI. I don't think the type PI is a factor for the crossline.

[harryk]

I have used normal master volume in front of PI and more and more different PPIMV variations in my Bluetone amps. I think that PPIMV is very useful when someone wants to get distortion also from PI, not only from power tubes.

[phsyconoodler]

I have tried the bootstrapped master in a Princeton circuit and I hate it.I might try Leevi's version.

[DummyLoad]

Poor results here also. My Matchless Lightning clone has a crossline MV and I find it almost useless in the bedroom. It may be more useful in a clube environment though. The lightning uses a LTP PI. I don't think the type PI is a factor for the crossline.

same here - i have accepted the fact that about 1/4 of maximum is about all the cross-line is good for with acceptable fidelity loss. IOW, don't expect it to turn a 15W amp into a 1W bedroom amp - it'll sound like doo-doo if you do...

peace.

--DL

[harryk]

I got very good results in my latest Bluetone Tweed Deluxe amp scaling the whole amp with VVR. I did not use any master volume and customer is very happy with that amp at the moment. I have done VVR to tens of amps and it seems that for some reason it works best with amps without negative feedback loop  .

[Leevi]

Harry, IMO the amps sound better without NFB even there is not a VVR inside.
/Leevi

[phsyconoodler]

That is pretty subjective.I prefer negative feedback in amps like the princeton reverb and super reverbs.Removing it is a cool tone to be sure,but it is better overall for my style with it in place.I like both,so I use a switch for both modes.

[FYL]

I have tried the bootstrapped master in a Princeton circuit and I hate it.

The Princeton uses a feedback loop which includes the concertina gain and PI sections plus the output stage and the OT. A bootstrapped MV - which modifies the gain of one of the stages in the NFB loop - isn't the best with these topologies, a nice type II PPIMV works much better.

[Leevi]

I use a switch for both modes.

I have also used NFB switch in many amps which I find very beneficial.
I have repaired lot of vintage amps and have noticed that in many of the them
the NFB has been disconnected. The switch gives the user possibility to
return to the original sound.
/Leevi