5E3 Output/Volume

[Tweed-amp-guy]

I've just completed a 5E3. It seems to work fine, suprisingly very low noise but, the volume knob - similar to another posting - seems to roll up slowly 0 to 2 then no change until about 8 or 9. Then, on 12 - cranked - I get good tone but I can easily have a conversation over the output volume. It's just not very loud. Is this amp really that quiet or is something likely wired wrong. I'm using the Mojo Tone transformers. OT Red wire tied to the standby and brown and blue to pin 3 on the 6V6s. Any ideas?

[hasserl]

No, it's not normal for the volume to be lower than normal conversation level. It should be loud enough to make your ears ring when cranked.

[Tweed-amp-guy]

Thanks - I suspected as much. Now, in checking some more I get a high frequency squeal when the bright volume goes above 11. Any ideas?

[Gee]

Thanks - I suspected as much. Now, in checking some more I get a high frequency squeal when the bright volume goes above 11. Any ideas?

There are 3 things to check. Grounds, Grounds and Grounds. If the volume is not there, then it could well be the speaker jack wiring. You can make up a piece of wire with an insulated croc clip on each end. Then, attach one end to one of the PT mounting bolts and try attaching the other end to points where there should be a good ground such as the speaker jack ground.

Does this behavior occur on all 4 i/p jacks?
Have you tried the 4 Ohm speaker jack with you speaker?

[Tweed-amp-guy]

Voltages high - output still low

I've got all grounds going to a pigtail which is soldered to an eye and bolted to the chassis. And, I've checked from multiple places to to ground and the resistance is less than an ohm.

I'm stumped - all voltages, starting at the supply wall voltage are 10 to 20% high. nothing really wacko, just all slightly high. Wall supply is 123vac

filament - 7.1 vac
pin 8 of 5Y3GT which supplies the circuit 432V. The Mission Amps schematic says this should be 391v. And the high v trend continues from there. Every voltage as compared to the Mission Amps schematic which I got off line is at least 10% high and in most cases 12%-20% high.

Any ideas?

Also, one of my 6V6 power tubes has a very slight white film around the bottom. Is it possible I fried this tube during testing? When I first fired this thing up all was well except the filaments were wired wrong. would this bad tube make cause this?

I get output, it's just not very loud.

Thanks!

[Bruce / Mission Amps]

The Mission Amps schematic says this should be 391v. And the high v trend continues from there. Every voltage as compared to the Mission Amps schematic which I got off line is at least 10% high and in most cases 12%-20% high.

Any ideas?

Thanks!

4-27-04....
I don't know what schematic you are looking at but, ... depending on the actual mains line voltage to the power transformer, my last 200 power transformers will run the B+ rail in the 5E3 kits at between 355vdc and 370vdc.
Plate to cathode will be about 20vdc less then that.

Is it one of my 5E3 kits or ? If so, just call me and we can walk though a few things.

[MWJB]

White film around the bottom of your tube indicates that you have lost vacuum for some reason, yes the tube is history. Your 6V6 tubes are being killed at these voltages with the stock 5E3 circuit.

If you don't have a higher voltage PT primary that you can use, you need to drop some B+ with a 50v 50W reverse polarity zener diode or rebias (larger 6V6 cathode resistor) & use modern 6V6s that will take the higher volts - the 2nd course of action will NOT result in "classic 5E3" tone however.

[Tweed-amp-guy]

Thanks - Bias question

OK, Thanks for the replies and offers of assistance and to Andy at Mojo for answering a question about the PT. I had a input jack wiring problem that cause a bit of a hum, but I guess my ears are the cause of the "low volume." My wife - and my neighbors - say this thing is plenty loud. Don't know, maybe I'm just accustomed to a lot more watts and my ears are a bit worn. That aside it still lacked punch or dynamics. So on to my next question.

Bias question. This is Cathode biased, right, so you adjust at the cathode resistor???

All of my voltages are still about 10 to 15% high across the board,

I measure across the Cathode bias resistor – 5W, 270 ohm (actually measure 266), 25V. Also had about 3.9 ma I calculated for the preamp.

25/266 = 93.9 ma

93.9 - 3.9 = 90 ma - (way high – right???) Not sure so somebody correct this before I ruin something.

I had a 50 ohm, 10 W resistor which I put in series with the 266 which gave me 316 ohms total. I now have 27.5V across the 316.

27.5/316 = 87 ma, minus the few for the preamp which gives me about 83 ma. Is this safe and are my calculations right?? The amp seem to have much more punch, a touch more head room, and the sustain seems better. That's only by ear but it sounds much better - playing with a Strat and Tele it's great.

I'm using JJ 6V6's.

Thanks

[MWJB]

Yes, you're going in the right direction. Ideally we need to work out plate dissipation by mutiplying plate voltage, less cathode voltage x plate current. But if you just gave us the plate voltage then that would help.

With the voltages that you quoted previously, I think that you will need to go higher on the cathode resistor (try 470ohms?).

[Bruce / Mission Amps]

Are you using a real NOS 5Y3GT or a Russian SOVTEK 5Y3?

If you are using the Russian one, it is not a "real" 5Y3GT but instead, more like a small bottle GZ30 from Europe.
This Russian rectifier is a fine tube but stiffer then a NOS 5Y3GT and will give you quite a bit more B+.

FWIW!!... I would not want to see 94ma at idle from my 5E3's 6V6s!!

The JJs can take more idle current then the 6V6EHs but you really can wear them out super fast running that higher current.
Keeping in mind the real 5E3 amps used a 100ma to 120ma power transformer, most all reissue 5E3 amps are using similar sized PTs, which you are now running almost clapped out with that high of idle current.
Too high of idle current = less head room in these.

Also, you didn't quite mention the voltage measured from lug 3 to lug 8 of the power tube.
These amps sound the best when the power tubes are idling around 11-12 watts each.

To get power tube dissipation numbers at idle, this plate to cathode voltage is the voltage used to multiply against that idle current number you derived.
In othe words, if you have 390vdc B+ at the tube socket, lug 3, then it would be 390v - 25v = 365v from plate to cathode.
Now it would be 93ma x 365 = 34 watts! Well, 17 watts per tube.
That is still way too high.
I'd be looking for somewhere around 34ma each.

#1 key here first, if you want more of the classic 5E3 B+ and tone, make sure you are using the NOS 5Y3GT.
It's OK to up the cathode resistor to as high as 330 ohms on these but I would not go any higher, instead figure out how to get the plate voltage lower.
If you are in Europe and using a PT with a multi-tapped primary, I'd try and run 220v on the 240vac taps if you can.
If not in Europe and the PT is wired for North America's 122vac... then it is time to look at a couple 9v-12v, 5 watt zener diodes installed in the high voltage secondary's center tap.

[Tweed-amp-guy]

Sovtek 5y3

Bruce, you hit the nail on the head. I'm using a Sovtek 5Y3. I've ordered a NOS and will report the results when I get it installed and check the voltages. And, if appropriate, I'll remove the extra cathode resistance I've added. Thanks!

[Bruce / Mission Amps]

It will soften the supply, drop the B+ by a noticable amount and give the amp a little more tweed tone squeeze too.

[Tweed-amp-guy]

NOS 5Y3GT installed

All is good. All voltages are spot-on and I've removed the extra resistance I had previously added to the cathode resistor.

Sounds great!

Thanks!