# 5e3 static issue

Discussion in 'Amp Tech Center' started by Q tip, Nov 17, 2019.

1. ### D'tarFriend of Leo's

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Never liked the push on spade connectors. Excellent spot for poor connections. Good ole soldered wire to terminal will eliminate a lot of future issues IMO.

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2. ### elpicoTele-Holic

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Okay well when you get conflicting readings like this it's always a good idea to get the calculator out and see what the numbers would really mean. Maybe that'll help tell which number is in error:

He measures 12.1Vac across the 8ohm speaker load. (12.1 x 12.1) / 8 = 18.3W

That's a little higher than the 12-15w usually quoted for a 5E3, but definitely in the realm of belief especially since the spec number is max clean output and he might be into overdrive.

How bout the other side of the output transformer?

780Vac x 2 = 1,560Vac across the primary

(1560x1560) / 8,000ohm = 304.2 watts

Now I've not seen any 5E3s that make 300 watts, and we already determined it only makes 18, so I'd wager one of those voltage measurements isn't right.

A good trouble maker reading this might say, "but maybe the primary impedance isn't 8K". I like the way you think. So what impedance would it need to be in order to transform the 12.1Vac he measured across the speaker into 1560Vac across the primary?

1560 / 12.1 = 128.9:1 (turns ratio)
128.9 x 128.9 = 16,621:1 (impedance ratio)
16,621 x 8ohms = 132,975ohm primary impedance

Okay, but we're getting good power out of the amp. Is a pair of 6v6 able to make 18watts of power if you load them with a 132K OT instead of 8K? That's a hard no.

So my question to the jury: do we believe this amp makes 300w? or that it has a 132k primary OT yet somehow manages to make good power? or that multimeters have trouble measuring the full tilt signal on a power tube plate?

Last edited: Nov 20, 2019
3. ### petebFriend of Leo's

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Great analysis Elpico.

I’m not doubting what you are saying in any way, I just have a few ideas on the subject.

It could be a multi meter reading wrong, or as is the case for measuring DC on the grid of the cathodyne PI, the measurement causes a consistent and predictable error based on the impedance of the meter.

I have never heard of trouble measuring (the high voltage) signal on the plate of a tube. I’ve measured signal on the plate of a power tube with both a guitar signal and a tone generator. I’ve never had trouble getting reasonable numbers, but my meter is not from radio shack either.

If a meter gives a bad number where it should not, I would suspect a bad connection and a low reading not high. It’s my personal opinion that if a meter reads 785 VAC it’s because there is 785 VAC present in one form or another.

I agree that it is a good sign that the voltage on the speaker is reasonable. It is a good sign that the power tube is probably within operating range, and the amp sounds good to show this as well.

Is it possible that there is a super high voltage on the plate and the OT can only pass what it can pass so the voltage at the speaker does not show that the plate voltage really is high?

Lastly, it was stated that the signal on the speaker (12.1v = 18W) could be more than max output (10 V = 12.5W) because the signal is most likely not a clean signal. This is different from what I found when I recently power tested for the first time on two different amps. It was only two amps but the results were very distinct, and it was very different from what I expected. All that happened is that when the wave reached full power, or close to it, the wave simply would not grow any bigger, it might fatten, but once it reached its upper limit it just flattened out. It did not look like a dirty signal, but a hard clip is a very dirty signal.

There is a recent thread describing this called “what causes hard clipping during power testing?”

Maybe my experience is different than others.

4. ### elpicoTele-Holic

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I should probably respond in that one then, I think we've taken up enough room in this guy's thread.

5. ### Q tipTDPRI Member

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Okay so I just ruled out the standby switch. Bypassed it still makes noise.
I'll try cold spray again on c10, c12, and c13 one at a time and see if anything hopefully changes and report back.
Just as a side note, those spade connectors are super tight. This amp although a 2007 is like brand new all jacks, sockets and connections are super solid. I cleaned all spade connections anyway just to be extra vigilant.

6. ### elpicoTele-Holic

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Nice, the list gets shorter...

7. ### PreacherFriend of Leo's

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Check those dodgey readings and update. I have a feeling it is something easy but those high readings are a little weird.

8. ### Q tipTDPRI Member

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OK so I have some new info. I was playing the amp tonight and thought if I got some good steady noise I would try my cold spray specifically on C10,C12 and C13. I got some noise as soon as I took my amp of standby and after about 30 minutes it was getting real noisy so I took a poke at those caps with the amp on. I happened to notice V3 was red plating and it looked like maybe v4 was just starting to also. Does that sound then like it may have to do with something in the bias section?(wherever that is?)

9. ### Burning FingersTDPRI Member

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R23 and C10 are the cathode bias components...check those.

10. ### elpicoTele-Holic

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Well that's not good. Your bias voltage (21.2Vdc) matches fender's spec exactly though. I wonder what's going on. You have a spare pair of tubes you can try right?

11. ### D'tarFriend of Leo's

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Tung sol 6v6 by chance?

12. ### Q tipTDPRI Member

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Yes I have a set of GE NOS that I tried in this amp about a month ago that I borrowed from my Tungsten Creama Wheat.(which runs higher voltages). The noise was still there. No noise in the Creama whatsoever. I've tried a set of NOS Raytheon's also but the noise was still there with those too.

13. ### Q tipTDPRI Member

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The tubes in there now are Tung-Sol but I have tried others and noise was still there. I suppose it's possible that it's 2 different issues though now that I think about it.

14. ### Q tipTDPRI Member

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I will measure the DC plate voltage today and post.
Thanks so far everyone.

15. ### Q tipTDPRI Member

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Measured my plate voltage: V3 366 VDC
V4 365 VDC

I tried to measure centre tap voltage off standby switch legs but got no reading so I tried off test point 1 and got 376 VDC but I don't know if that actually gives me the centre tap voltage or not.
I then measured the resistance from pin3 of V3 and V4 to test point 1(X36 4.7k 2watt resistor) and got this. Although the measurements varied around 5 ohms at first after about 5 minutes it seemed to more or less settle on these.
V3 215 ohms
V4 214 ohms
From what I have read these readings should be in the 50-70 ohm readings so I guess I did something wrong.
*Note
I left the same 6v6's and didn't leave the amp on for more than 10 minutes so in that time I saw no red plating. Lots of noise especially for the first 5 minutes or so.

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16. ### Q tipTDPRI Member

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OK so I took the Tung-Sols out that were red plating and put some Electro-Harmonix tubes that I had laying around that are basically brand new and played the amp for about an hour. For the first 10 minutes there was a lot of noise and then after 30 minutes or so a bit less noise, intermittent popping with crackling and once the volume jumped up a like having my guitar on 6 then 10. Then after 45 minutes no noise at all. No red plating throughout either. At one point my guitar started buzzing but only when I put my hand on the strings but that went away after a few minutes too.
Anyways the main thing is it seems like the output tubes happened to die and there seems to be no red plating for now.
I don't know what is going on but because it's so intermittent I think if I took it to another tech that nothing would happen. Like the frog that could sing and dance in bugs bunny(hello my darlin' hello my baby etc) but would only do so when no one else was watching.
I checked plate voltage on both tubes and poked at pin 3 and wires going to them while staring at my meter and voltages stayed stable.

17. ### elpicoTele-Holic

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Wait, it killed the EH tubes? Something strange going on. Try disconnecting C10, if that cap is bad it could explain the gain jumps. You could also try clipping a small cap across the power tube pin 3s to rule out HF oscillation, but you need a nice high voltage one. edit: it would probably be better to use two and clip them from pin three to C13

Last edited: Nov 24, 2019
18. ### elpicoTele-Holic

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And I hate to say it but it might be tech time. This has turned into something different than the original situation of "my amp makes static noises sometimes". If damage is being done to parts now I think you have to consider whether it's worth it to try to fix it yourself.

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19. ### Q tipTDPRI Member

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It didn't kill the EH's but noise was still there. No red plating though after about an hour of use. The Tung-sol reissues red plated. It might just have been their time.
If I disconnect C10 would I then need to run plain wire in it's place and if so how long can I run the amp that way?
Thanks

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