59' reissue troubles, cracks and hisses

[hank40]

My bassman is a 5f6-a model and first of all does not have a 5ar4 tube in it. but has what looks to be a black circular plug in place of it. should i be concerned?

Also when it is switched on it hums loudly and pops and crackles. i can hear my guitar thru it but it cuts in and out and sounds like the speakers are blown or something. i also have to crank it up to 8 or more just to hear the guitar at all. And when i turn it up and play it pops loudly.

Any thoughts?

Ive tried switching the 12AX7' around but the problem is still the same.

Thanks

[MWJB]

"My bassman is a 5f6-a model and first of all does not have a 5ar4 tube in it. but has what looks to be a black circular plug in place of it. should i be concerned?"

Sounds like the SS plug in rectifier that comes stock in pre "Ltd" RIs. You could try a 5U4GB for a warmer tone, bias current will drop & may need adjusting. 5AR4/GZ34 rectifier is what came in the original amp, but these have a high failure rate in pre "Ltd" RIs.

My first guess would be burned up plate resistor at the PI tube (12AX7 next to the 6L6s), maybe a failing 100K feeding the cathode follower stage, maybe a blown screen grid resistor. All these things are quick & cheap to repair.

Tube sockets might also need tensioning, turn the amp full up (inc. tone controls) & gently wobble the 6L6s in their sockets, any untowards pops/bangs?


Best to double check tubes & use a known good 12AX7 from another amp, in place of the ones that came with the amp. You can try one power tube at a time, see if any symptoms follow the tube or the socket.

Don't mean to cast aspertions on your trouble shooting & repair skills but are you comfortable reading high voltage dc/aware of usual safety precautions when working around tube amps?

[hank40]

Thanks for the thoughts. No i am not used to working on amps and reading voltages. I just thought maybe there would be a simple fix. I do have a blues deluxe maybe ill try the 12AX7's from that one on mine.

dumb question but can i test out the 12AX7's from another amp on mine using one at a time or do they all have to be plugged in for the amp to operate correctly.
Ya im pretty sure my RI is not a LTD. i think its a earlier model.

[hank40]

I checked the fuse and the fuse had been blown. so i put a new fuse in it and had the volume up pretty high and i was looking at the 6L6's and one o them got bright orange very quickly and shot a white light and looked as if it exploded inside of the tube. i turned it off and checked the new fuse and it was blown.

any thoughts on what the reason for this might be. thanks

[Enzo]

Actually, my first thought was that your power tubes are failing. Pops and crackles are usually a sign of failing power tubes.

Now you have blown fuses. THE most common reason for fuses blowing in tube amps is a bad power tube.

ANy time you have fireworks inside a tube, it is bad.


All in all I'd say you need new 6L6s.

[hank40]

Thanks for the advice enzo. ok if you know off the top of your head how much the 6L6's run for?

[acorkos]

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