Please help with 5E3 build !

[MHProd]

I finished a 5E3 ish build and here are some measurments (amp on, all tubes in):

5Y3:
pin2: 340VDC
pin8: 340VDC

6V6:
pin3: 340VDC
pin3: 340VDC

All heaters ared 6.3VAC

Board from left to righ:

16uF#1: 340VDC
16uF#2: 340VDC
16uF#3: 250VDC
1M: 35VDC
1K5/.047uF: 84VDC
56K/.047uF: 180VDC
100K/.022uF: 109VDC
1K5/25uF: 2VDC
100K/.1uF: 163VDC
100K/.047uF: 144VDC
2K7/.68uF: 1.90VDC
1K5/25uF: 1.50VDC

Cathode resistor is 660 ohms (!) to get the the bias to 22mA.

PS: The Tung Sol RI 6V6s I use are rated at 12W max dissipation.

The volume/tone pots are wired like a 6G3 and I use a 6H choke instead of the 5K6 resistor.

Split cathode on V1 like a Super Lead.

The amp doesn't distort much, no bright cap on the pot since I already have a lot of top (strange).

The break up isn't great, the highs become buzzy/farty sounding. I use a 470 Ohms resistor between pin 4 and 6 of the power tubes and a 1K5 between pins 1 and 5.

I used this layout:
http://stvnscott.websitetoolbox.com/file?id=532328

Is there anything that looks suspicious in the voltages above ?

Should I measure something else ?

[txstrat]

On your layout the point (c) - on the second filter cap - should go to pin 6 of the 6V6 tubes instead of pin 4. To let them 470 ohms resistors have a purpose.
660 ohms is way too high IMHO. The schematic says 250 ohms. If you don't wanna run the amp too hot you might try a 330 or 390 ohms for a start. The higher the resistance the 'colder' you run the amp. Running the amp too cold could result in a harsh and rasping sound.

And welcome to the forum, BTW.

[MHProd]

Thanks mate.

Actually, I measured the B+ on pin 3 of the power tubes sockets with the tubes out, and I get 405V.

I changed the cathode resistor to 440 Ohms so the tubes give a bit more than 10W of power.

Hmmm, interesting about the the change to pin4 to pin6.

The other odd thing is that I don't have a lot of gain (a lot less than my original 5E3).

[txstrat]

Originally Posted by MHProd

The other odd thing is that I don't have a lot of gain (a lot less than my original 5E3).

I believe that'll change with the 'smaller' cathode resistor. The power tubes can't run hot enough right now and don't get into saturation, hence less gain. Are the values in the preamp just like stock? Double check.

[tubeswell]

With cathode bias, you can run the output tubes flat out without hurting them - so try 250-270R and see how you like the sound.

[MHProd]

Thanks guys.

As I said, with the 440 Cathode R, I get a dissipation of 10.2 watts on the tubes. The Tung Sol reissue 6V6s are rated at 12W max plate disp. (not the usual 14).

So I guess it's pretty good.

I will try some Zener diodes to drop the B+ on the plates.

BTW, the transformers are Mercury Magnetics.

[black_labb]

Originally Posted by MHProd

Thanks guys.

As I said, with the 440 Cathode R, I get a dissipation of 10.2 watts on the tubes. The Tung Sol reissue 6V6s are rated at 12W max plate disp. (not the usual 14).

So I guess it's pretty good.

I will try some Zener diodes to drop the B+ on the plates.

BTW, the transformers are Mercury Magnetics.

I triple checked my wiring and If I plug the amp straight into the wall, it gets the filaments to 8VAC ! I use a Variac to bring them down to 6.3VAC (variac on 110V).

Do you have any idea why I would get too much volts on the filament ? What kind of mistake in the wiring would create this ?

i dont know what kind of problem could do that, 8v is 25% higher than 6.3v, not an insignificant amount. what was the wall voltage at when you had the voltage at 8v? would have been 137.5 or so calculating it, which isnt what you should have at the socket. there shouldnt be a tap to give those voltages.

how was the amp sounding when you had the transformer running at the right voltages? it could have been running well with a correctly valued cathode resistor to suit the lower voltages.

[tubeswell]

What goes in comes out - in this case, the higher filament voltage is the result of your higher wall voltage.

It really doesn't matter if you run 6V6GTs at 12W in a cathode biased PP amp. You'll get better saturation - if that's what you want.

I'm reminded of one of Bruce Collin's opinions on the subject here;

http://blueguitar.org/new/text/threa...%20Biasing.pdf

[MHProd]

Filaments are actually 6.8V (sorry I forgot the 6.). Wall is 120V most of the time. So obviously, it's not a big deal.

I will try to get as close as 12W disp. as possible.

I rewired the 2nd cap to Pin 6 instead of Pin 4. I was wondering why I STILL had treble oscillation with a 3.3K grid resistor !!

I wouldn't mind adding an extra Tone pot too (Right now the pots are wired like a 5E3, not 6G3). In that case, should I solder leg 3 of each volume pot to pin2 of V2 ?

Anyway, I'll see if all that makes the amp sound better and I'll post the results.

Thanks Again !

[txstrat]

Originally Posted by MHProd

In that case, should I solder leg 3 of each volume pot to pin2 of V2 ?

NOPE.
Put a 220k mixing resistor after each vol pot wiper like in the 6G3 schematic. The two signals paths need to be separated from each other.

[MHProd]

Just to be sure, to measure the B+, I check to pin 3 of the power tubes with the tubes out, right ?

When the amp isn't plugged in the Variac, I get 435VDC !

I changed the cathode resistor to a 390 Ohms, so I get just over 12W of disp.

If I check the B+ on pin 3, I now get 310VDC... Is that normal ?

[txstrat]

Tubes out means no load and therefore higher voltages. Measure with the tubes IN the sockets.
Voltages within reasonable areas (+/- 10%) are no problem at all.
Go for the ~270 ohms resistor like tubeswell proposed and don't mind the dissipation of anything.
Every genuine 5E3 runs at 250 ohms and around 350v (+/-) of plate voltage AFAIK.
There should be no problem.

[MWJB]

Whoa! Slow down...

"When the amp isn't plugged in the Variac, I get 435VDC !" Is that with or without tubes? With no tubes installed & no variac that sounds about right. What do you get with a 330ohm cathode resistor, tubes installed and the amp plugged straight into the wall? The larger the cathode resistor you use, the greater your plate voltage will be.

There's little point in measuring B+ without power tubes drawing current, you don't get a realistic reading.

"If I check the B+ on pin 3, I now get 310VDC... Is that normal ?" 310v is not normal in a 5E3 style amp, for example Fender's 57 Deluxe amp runs 390vdc with stock tubes & rectifier, it also uses Russian 6V6 tubes (EH).

If rebiasing has knocked 125vdc off your plate voltage (435-310v, amp NOT plugged into variac in both cases) then no, that's not normal.

But if rebiasing has knocked 30vdc off your plate voltage (340-310v, amp IS plugged into the variac in both cases) then that might be normal.

I don't think that you need the variac at all from the voltages you are quoting.
If it is just the heaters that are concerning you, then be aware that tubes are designed to see "6.3 to 6.9VAC", many vintage Fenders are around the 7VAC mark.

[MHProd]

So that means I got it all wrong...

OK, so with a 270 Ohms cathode R, I get 322V B+ on the plates.

20.3V accross the cathode R.

[MWJB]

Is that without the variac?

[MHProd]

That's without the Variac.

[MWJB]

Looks good, you could even try more B+ with a 5V4.

I'm always in favour of determining plate current with bias probes, but even by using the cathode resistor method, you appear to be well on the safe side with regards to current.

20.3v/270 = 75.2mA
75.2mA/2 tubes = 37.6mA
37.6mA * 302vdc (remember to deduct cathode voltage from plate voltage) = 11.4W ..then deduct about a W for screen current = 10.4W.

But as TX Strat points out, I wouldn't really be worrying about the tubes running over dissipation, with a 250/270ohm cathode resistor, until your plate voltage was well in excess of 380vdc.

[MHProd]

The 435VDC I had was with no tubes plugged into the wall.

The amp sounds much better now, huge deep solid low end. However, I still don't have that much gain... The amp starts to break up at 12oclock with my 335 !!! Around 3oclock with a strat or tele.

I put a 12AX7 in V1 but it still could get a bit more... I put a 5U4 rectifier in there that gave me a 345VDC B+ (instead of the 322VDC with the 5Y3).

The amp is kinda bright (even though there is no bright cap !!) and when I push the volume, I still get some buzzy, cringy sound in the high end when I play a full chord (some sort of buzzy noise that dies quickly).

Any clue why it'd do this ?

[MWJB]

Do you have an updated layout? Your layout shows bright caps galore, though you say you have none? You said early on that volumes were wire like a 6G3, then later you said that they were wired like a 5E3. Volume II on your layout would appear to be wired wrongly in any case.

Some photos of the actual build would be good, so that we can see what you have actually done.

5U4 is not a good choice for a rectifier in a typical 5E3 style amp, unless that you know for sure that you have a 3A 5VAC rectifier winding (most 5E3 style PTs only have a 2A winding).

[MHProd]

I added an extra tone pot.

Ch1: Volume pot is wired like a 6G3 (220K from leg 2 and leg 3 goes to bypass cap).
Ch2: Volume pot is wired like a 5E3 (leg 2 goes to bypass cap and leg 3 to 220K)

Both 220K Rs go to V2.

I noticed I put a NOS 12AT7 in V2 and I changed it to a JJ 12AX7 and I get more distortion. All the time, I've had a 12AX7 in V1. However it still doesn't distort like my original 5E3... and the amp is much brighter for some reason... I guess it's probably due to the Merc Magn OT.

Right now, the tone/volume pots have a 250pF cap accross them.

Do you guys have any tricks to try out... ?

[MWJB]

"Right now, the tone/volume pots have a 250pF cap accross them." Where exactly accross them? Are these 250pf caps in addition to the 500pf bright caps in the stock 5E3 & 6G3 circuits?

[MHProd]

No, each tone control has a .0047uF to ground cap on leg 1 and there's a 250pF cap between leg 3 of the tone pot and leg 2 of the volume pot.

Very bright overall and on the 5E3 channel, the tone pot doesn't add gain like an original 5E3... I'm pretty sure my wiring is good...

[MWJB]

Why 250pf, not 500pf.

Your 5E3 does not have a choke, hence the difference in voltage between plates and screens afffects tone.

Do you have a pic of the pot wiring?

[MHProd]

250pF because 500pF would make it even brighter ??

And yes, the amp has a choke.

Sorry no pics right now, but I explained how I wired it...

[MWJB]

250pf only allows certain higher frequencies through, compared to 500pf.

"but I explained how I wired it..." not that I doubt your wiring skills, but it's always nice to what people have ACTUALLY done, as compared to what they THINK they have done.

If you wanted your latest amp to sound just like a 5E3 then you wouldn't have used the choke, your screens probably run about the same as the plates (like a tolex amp), not 30-40v odd below the plates (like a 5E3).

[MHProd]

Oh you can doubt my wiring skills !! I doubt them myself...

I just don't have a camera handy right now.

I tried without the choke too but had the same result... (bright, not much distortion).

[tubeswell]

Can you draw a layout of your wiring and post that maybe?