73 Superbass Issues (fuses blowing)

[dan_tramble]

Hi all

I have my good buddies 73 PTP Superbass here. Initially it was blowing the mains fuse. I took the amp out and retubed it with a brand new quad of JJ EL34 I have on hand. The plate voltage was 512 and I set the bias accordingly. I replaced the mains fuse when I changed the tubes as well.

Ran the amp and (he uses a hot plate ok) it's 16 ohm just like the output load

I ran it loud and then the power indicator started to "dim and load" with my guitars input ok. I'd strum and you'd see the light drop and go up. (Like a visual current indicator). The output volume was "wavering" and the HT fuse then blew. I stopped at that point.

I put the proper spec SB time delay fuses in it. I think the filters might be dried up and the bias caps as well.
I realize this could be a bad PT possibly as well

The amp is 125% original. Everything. He got it from ROYAL BRIT and it looks like it came from the original owner or from a umplayed collection. It's immaculate

Has original bias caps, all original Daly filters. The dye joints are 125%. The board was never lifted

I am thinking I should replace the bias caps and the filters...

Am I correct here in my logic?

Please advise and sorry for the dumb questions

Regards

Dan

[Haze13]

Caps can blow the fuse. When you strum - they are discharging, but than they need to be charged again, and that's where their ESR kicks in... The rule of thumb is to change every electrolytic cap in a old amp. They die. That's it... If they die, they need to be replaced.

[dan_tramble]

That's exactly what I am thinking as well. I have 6 x 50/50 F&T caps here and 2x Vishhay 10 uF bias caps here

I've already started to take apart the amp cap by cap and I want to get it clean as possible.
I've redid some jumpers on the 4 caps and dyed the joints

I just want it 110% clean.

I am going to do a full valve change afterwards and bias it to 70%

Thank you for your advice

When the HT fuse popped I realized that's it and it's going to have to need some SERIOUS SURGERY!

[dan_tramble]

Replaced 6 x F&T 50/50 and 2 x Vishhay 10 uF bias caps and did a full revalve

Set the bias at 33 and played it and it's fixed!!

Thanks for your help!

Dan

[Haze13]

No problem! I'm glad that it helped. Rock on!