1959RR blew power cord fuse (5A)

1987XPW, 1992LEM, 1959RR, 2203KK

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munkyver
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1959RR blew power cord fuse (5A)

Postby munkyver » 19 Oct 2016, 21:01

Hi guys,


I replaced all the big capacitors of my 1959RR because I thought that the noise is coming from them. (i know I am a newbie with tube amp repair). I retubed it as well with EL34EH and biased it to 33mA +/- per tube. Anyway, all was good until I plugged in my THD attenuator and both volumes of the 1959RR at 8. The amp sounded so good with the Hendrix cabinet then I saw two tubes lighting so bright and caput goes my amp.

I was so worried that I baked the transformer and the PCB as I saw in another post in the internet. I plugged the amp again but no light coming from it when I switched it on. So logically, I thought of the wall power if there was electricity and there was. So the next thing that I checked was the power cable. I tried another power cable and it worked. Good thing that the power cable that I am using has a fuse.

So i fired up the amp and it was working.

When I connected the bias probe, the reading was the same at 33mA. I started playing and put the volume to 4 and the bias reading came up to 70mA. I don't know if this is normal. Further on I put the volume up and the bias became higher again. Is this normal for a non master volume amp?

Cheers,

Anitoli
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Re: 1959RR blew power cord fuse (5A)

Postby Anitoli » 19 Oct 2016, 22:33

You do not check the bias with a signal applied as the fluctuation (AC) will throw the reading off. Always check bias with no signal.

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Re: 1959RR blew power cord fuse (5A)

Postby munkyver » 19 Oct 2016, 22:41

This is what I am using for biasing:

https://www.eurotubes.com/store/pc/view ... category=6

do you think it is ok?

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Re: 1959RR blew power cord fuse (5A)

Postby Anitoli » 20 Oct 2016, 12:51

I think that would be fine. I like the fact that it shows you the plate current and voltage. This will enable you to get a more accurate reading. You just multiply the current times the voltage and you get the plate dissipation. For example 35ma x 460v = 16.1w.
(.035 x 460 = 16.1w) It is that simple.

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Re: 1959RR blew power cord fuse (5A)

Postby munkyver » 20 Oct 2016, 19:47

Hi Anitoli,

When I used this bias probe, I got the readings of each of the four power tubes. They are in the range of 32 to 33mA, this is when both volume 1 and 2 are on zero. Did I do it correctly? the volts is 455v.

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Re: 1959RR blew power cord fuse (5A)

Postby Anitoli » 21 Oct 2016, 02:17

Yes, volumes on zero is correct/no signal applied. Your idle dissipation at those numbers would be 14.6w- 15w. You could go up little if you wanted but if you like the tone there is nothing wrong with those settings. Remember it's never a good idea to exceed 70% of the tubes maximum dissipation as this will set the bias too hot and greatly shorten tube life.

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