5e3 problems

[stretch2011]

It has been working fine for the last year. Was playing the amp, put it on standby, turned it back on and my volume was halved. I had a 6v6 red plating. Replaced the red plating sovtek with a jj and no more red plating. I'm running around 400v on the plates and the screen is about 15v higher. I am using a 470R resistor between pins 4&6 and a 1.5k between 5&1.

Then I noticed that with the volume at 11 its loud, but at 12 its Super quiet. I had the ct wired to the standby like the original layout, which caused a surge when flipped, so I rewired that and replaced the rectifier.

The problem still persists. With either volume at 12 I get severe volume attenuation. Any ideas?

[xtian]

Sounds like your volume pot is fuxxored, doesn't it?

[frankdrebin]

it could be parasitic oscillation,that is also one of the major cause for ouput tubes and transformer failure.

[stretch2011]

Both volume pots? I bought cts pots, and honestly might have 50hrs on the amp. If I plug into the bright channel and turn it up its fine. If I turn up the normal channel all the way it cuts volume while I'm plugged into the bright channel. It works vise versa with the channels.

The amp hums but nothing outlandish. With the guitar unplugged its pretty well dead quiet while turned up.

[JazzGuitarGimp]

The volume pots in the two channels of a 5E3 are interactive. It is working correctly. Try plugging in to the bright channel, and set the bright volume at 5, then slowly bring up the normal channel volume - it's very subtle, but there is a noticeable boost in the bass as you bring the normal volume up (until you go too far and attenuate the signal). It's a very old trick with the 5E3. Do a google search for Tweed Deluxe Volume Interaction, and you will find a wealth of information about this.

[stretch2011]

Right before you replied I concurred this. I just finished up another 5e3 for a buddy of mine so I tried it with his, the exact same thing.

On parasitic oscillation, I'm intrigued.

This new 5e3 I finished has the bacon frying sound when turned all the way up with a guitar plugged in and all the way up. I turned off all the lights in the room and chop sticked around in the amp. The only thing that changes the sound is if I go anywhere near the input jacks *without touching them*. No guitar plugged in, pretty much dead quiet.

Is this bacon frying parasitic oscillation?

[frankdrebin]

If you turn up the unplugged input volume it loads down the signal,almost clean yes,if you turn it to zero you get maximum output.
Frying,well any amplifier cathode biased being at full current on idle has the tendency to sound like that,it comes both from tubes and resistors.

[pdf64]

I'm running around 400v on the plates and the screen is about 15v higher. I am using a 470R resistor between pins 4&6 and a 1.5k between 5&1.

Then I noticed that with the volume at 11 its loud, but at 12 its Super quiet. I had the ct wired to the standby like the original layout

This doesn't seem to be a 5E3; 5E3 screens are way lower than plates, and don't have a failure inducing standby implementation done without due consideration for rectifier current limitation.
To describe is as something it's not likely results in wasted time for all concerned.
For valid responses, a schematic, implementation pics, and a voltage survey at idle would be very beneficial.
Otherwise a whole lot of assumptions are required.

it could be parasitic oscillation,that is also one of the major cause for ouput tubes and transformer failure.

Yes, oscillation seems a likely possibility if (again, not a 5E3) a 12AX7 rather than 12AY7 is fitted in V1.
But my suspicion is that if so, it would more likely be the free running ultrasonic variety, rather than parasitic to a signal.

Generally, commercial amps don't run 2 cascaded 12AX7 triodes totally wide open / no interstage attenuation, without there being mitigation for oscillation. The 57 Deluxe RI (unlike a 5E3, the stock V1 tube is a 12AX7) maybe the only exception to that.
I suspect that it must have been laid out very carefully; with a potential for a voltage gain of ~3600 (71dB), a response extending well into the ultrasonics, several polarity flips, and a fairly tight chassis, I'm surprised more builders don't mention the issue.

The screens being 15V higher than the plates may significantly increase plate current / dissipation, compared to a 5E3; so they may have been running well over their limiting value.

[pdf64]

I just finished up another 5e3 for a buddy of mine so I tried it with his, the exact same thing.
...
This new 5e3 I finished has the bacon frying sound when turned all the way up with a guitar plugged in and all the way up. I turned off all the lights in the room and chop sticked around in the amp. The only thing that changes the sound is if I go anywhere near the input jacks *without touching them*. No guitar plugged in, pretty much dead quiet....Is this bacon frying parasitic oscillation?

If V1 tube is a 12AX7, I suspect that it may be the audio impact resulting from ultrasonic oscillation; what happens at various settings of the guitar's volume control?

I guess you used the same layout / lead dress for both amps? There may be room for improvement with it, that may act to suppress positive feedback loops.

Good photos of the implementation would be helpful in identifying specific changes.

[The Ballzz]

Has anyone ever seen a schematic for the re-issue? I wonder how close it is to the original? I currently have a chassis and output transformer waiting for the rest of the components for a new build.
TIA,
Gene

[martin manning]

The schematic and chassis layout ('57 Deluxe) is available on Fender's web site. It has some modern improvements like additional fuses and an NTC thermistor, but it is otherwise like the original.

[stretch2011]

12Ay7 in the first position.

Aside from the 470 screen resistors on the 6v6's, a more modern standby wiring, and a hopped up power transformer it's a stock 5e3. The pt is from a 65 deluxe reverb.

I'm racking the noise up to the carbon comp plate resistors.

I'm going to do some things with the power supply to see if I can get the screen voltages to go down.

[Structo]

Are you using a tube rectifier?

Too late now but I don't put standbys on the small amps these days.

No need.

What happens is you probably have the standby between the rectifier and first filter cap.
So you when flip the switch there is a huge current demand for an instant and some components can't take that shock over and over.

I like having the big reservoir cap before the standby switch, so that cap charges as the tubes warm up.
Then when you flip the standby off, there isn't that big demand for current.

[pdf64]

Aside from the 470 screen resistors on the 6v6's, a more modern standby wiring, and a hopped up power transformer it's a stock 5e3

I don't see how 5E3 screens can be 15V higher than the plates; 4k7 will drop some Vdc.
Are you sure that there isn't a choke instead on the 4k7 / 5k screen grid B+ dropper?

There's no standby in a 5E3, what is meant by modern?.

Voltage survey at idle?

[The Ballzz]

I think stretch2011 is referring to the "modern" Fender "57 Deluxe/Fender 57" schematic, which does have a standby and 470R screen resistors that are not on the old, original schematic:

http://www.fmicassets.com/Damroot/Origi ... matics.pdf

Just Sayin'
Gene