Bassman 59 RI

[glasstone]

Hey

I have a bassman 59 RI tweed, the problem is, that it distort really nasty when played.

I have checked everything resistors in the preamp and power section, checked the output trafo.

When I measure volt on pin 3 on the powertubes and play the voltage drops.

Any ideas?

Thanks

[Enzo]

That is normal. ANything that draws power from the supply will cause the voltage to sag.

Try connecting it to a different speaker for test.


Look CLOSELY at the solder to the power tube sockets for cracks - or just resolder them.

Look at the phase inverter tube, pins 1 and 6. Is there roughly 275-300vDC on each? And pins 3 and 8 should be wired together, and is there about 40v on them?

[glasstone]

Hey Enzo

Tried different speaker, all solderjoints are checked and resoldered.

I know that there is a little sag in voltage from supply, but this goes fra normal to very low, aprox half.

I was thinking filtercaps, could that be the an option for this problem?

Phase inverter checked, all good.

[Chuck H]

It sounds like the amp may be incorrectly biased. You need an ammeter on your meter or a small value resistor, between one and ten ohms, to check your bias.

You say the distortion is nasty. Does that mean it sounds abnormal or just not good to your ears? is the distortion buzzy/phasey or like a sharp intermittent crackle. Please describe nasty.

[pdf64]

'When I measure volt on pin 3 on the powertubes and play the voltage drops.'
Not a good place to measure with a guitar signal - there is likely to be a massive signal voltage, may damage your meter.
To assess sag, measure the Vdc at the rectifier output under static and max clean signal conditions.
Pete.

[tubeswell]

How old are the output tubes?

[mac1amps]

FWIW, I've heard similar complaints with those (RI Bassmans), which turned out to be the speakers. The earlier reissues all used those lightweight Eminence AlNiCo 10's, which actually sound decent when they're new, but they don't hold-up to higher volume levels for very long (especially with humbucking pup guitars, and/or running the Bass control at higher settings). Then there's also the reissue [Italian made] Jensens that don't "deliver" like the old ones did.......'time for some Webers!

[jonamojo]

I had one of those early bassman ri for one they have too much filtering 2 they have too much b+ I used a zener diode to bring down the B+ and redid the filtering and guess what it still sounded like crap. Never got around to changing the speakers but I suspect that was where most of the problem lies.

[JoeM]

Too much filtering? I had one and increased the filtering on the screens and it tightened it up a bit. Mine had the earlier Emi Alnicos. Good power tubes needed for the B+ with the SS rect is close to 500V.

[jonamojo]

i was using 5ar4, way goal was to turn the ri back to 59 specs, as I recall the pt put out 40 more volts than the original. the filtering in the preamp was double. I yesed janphillips 6l6wgb I also installed a bias pot. I had a friend with a real 59 and I bought my fluke over to take measurements,and then went about my mods. And SS in a 59ri? doesn't sound like the tone I was going for, I also installed 200 ohm sag resistor between the recifier and the B+. After the rectifier your lookin at 432volts on the plateswith 40uf 430 on the screens with 20uf after the choke you got 20uf feeding the pi now you down to 385 the pre only has 8uf at 325 seems like were on the wrong planet.

http://www.singlecoil.com/docs/bassman.pdf

[JoeM]

Early RI Bassmans came with an SS rectifier, they were mounted in a plug for the rectifier socket. Mine definitely didnt sound like crap, really a great sounding amp. I dont like sag in an amp anyway since I play clean nearly all the time. Original Bassmans had much higher voltages than what's shown on a 5F6A schem anyway.

[jonamojo]

check out the 59ri you speak of http://support.fender.com/schematics..._schematic.pdf even with a GZ34 ri voltages would still be higher you don't like sag I don't get it I'm new here so you don't like the original specs and the statement about original bassmans have higher voltages is just wrong its cool if you like 500 on the plates but there are know vintage bassmans with 500+ on the plates where are you getting this info or are you just pulling my chain I've restored 3 over the last 12 years and none came close to 500+ in summary the 59ribassman isn't a vintage bassman nor does it sound anything like one maybe I should tell neal young his deluxe is the same as the reissue he just needs a weber copper cap and a new power transformer i'd love to see the look in those ice cold blue eye's hahahah peace bro

[Jazz P Bass]

Try throwing a well placed 12AU7 in the preamp.
These RI's have absolutely no control.

[JoeM]

check out the 59ri you speak of http://support.fender.com/schematics..._schematic.pdf even with a GZ34 ri voltages would still be higher you don't like sag I don't get it I'm new here so you don't like the original specs and the statement about original bassmans have higher voltages is just wrong its cool if you like 500 on the plates but there are know vintage bassmans with 500+ on the plates where are you getting this info or are you just pulling my chain I've restored 3 over the last 12 years and none came close to 500+ in summary the 59ribassman isn't a vintage bassman nor does it sound anything like one maybe I should tell neal young his deluxe is the same as the reissue he just needs a weber copper cap and a new power transformer i'd love to see the look in those ice cold blue eye's hahahah peace bro

I dont care if you 'get it' or not. The amp worked great for me. I think you've only seen the published voltages on the schem.

[jonamojo]

I dont care if you 'get it' or not. The amp worked great for me. I think you've only seen the published voltages on the schem.

well it's another day lets just squash it bro I'm glad things are working out for you with your amp. Take it easy.....J