Fender bassman 100 blowing fuses

[Jam]

I have a old Fender bassman 100 blowing fuses so I took out the 4 6L6GC output tubes and put a new fuse in and it stays powered up. So I think Im on the right track? So what are good tubes to buy? Where? Should I replace all of the tubes or just all the output ones? What do they mean matched? Thanks for any info

[Chuck H]

You need to find out why the amp is blowing fuses. It may be a bad power tube, or tubes. It may also be a failing bias supply or a shorted filter cap. Just plugging in new tubes may cost you extra money, not fix the problem and perhaps even damage the tubes you just bought.

If you DO need tubes, buy a matched quad.

To be perfectly honest I haven't had much luck with new power tubes from a couple of the well known distributors lately. The set that's giving me the least amount of trouble are Ruby tubes. So I'll recommend those. Make sure whatever distributor you buy from honors Ruby's excellent warranty.

Unless you're having trouble with the preamp tubes you don't need to replace them.

[soundguruman]

I will never buy ruby tubes ever again.

IMHO JJ tubes are far more consistent.

[Chuck H]

I will never buy ruby tubes ever again.

IMHO JJ tubes are far more consistent.

Yeah? The Ruby's operating in my customers amp now replaced a pair of JJ's where one shorted the moment the amp was clipped. Mine and your opinions are based on very low volume purchasing though. JJ's warranty and any warranty offered by their distributors is for $h!t. The Ruby warranty virtually guarantees useful tubes for the purchase price so that's what I based my suggestion on.

[Enzo]

The Ruby 6L6GCMSTR has been a consistent winner, I have yet to get a bad one and I have been using them since they came out. I don;t hesitate to recommend them for any 6L6 applicationj.

And for our never Ruby again only JJ guy, the Ruby 6L6GCCZ ARE JJs. So you can buy JJs with the Ruby name on them and get the Ruby warranty.

There are several threads around this forum wherein guys have griped about the poor quality of their JJs, I don't see the same threads for the Rubys.

[Chuck H]

And for our never Ruby again only JJ guy, the Ruby 6L6GCCZ ARE JJs. So you can buy JJs with the Ruby name on them and get the Ruby warranty.

SGM was probably talking about the typical Ruby selected Shuguang tubes. Which is what I have now and they sound good except for a tiny bit too much microphony for the combo they're in. They'd be golden in a head cabinet. I will be replacing them with the same tubes purchased under the warranty so I can return them if they're also microphonic. Being a little microphonic is a lot better than failing instantly within spec. Which three other tube brands did. And yes, I considered that it was the amp eating the tubes, but no. Just a lousy, unlucky coincidence in this case.


I'd be happy to spend a little more on the Ruby selected JJ tube if I wanted the JJ tube, get the good warranty and potentially save a lot of down time. That's worth the extra $15 a pair every time!

[Justin Thomas]

Back to Chuck&s point in post #2...
Hey Jam, have you visited here yet?

Tube Amplifier Debugging Page

Gotta find out why it's blowing fuses first! Could be a bad tube, but no new tube warranty covers a defective amp! At least, not that I've found... good luck!

Justin

[Chuck H]

Thanks for reiterating the importance of that suggestion.

Incidentally, that quote you have credited to me is actually a Jim Carrey line. I can't remember which movie. It's funny though

[g1]

Incidentally, that quote you have credited to me is actually a Jim Carrey line. I can't remember which movie.

Ace Ventura, but he said "spank you".

[Justin Thomas]

Quote fixed, and of course your use of it here was impeccable...
Let's just say I learned about the tubes/fuses thing the expensive way!

Is this a personal amp or a friend/customer's amp? If you get an old amp that needs new tubes, it probably needs new "OTHER STUFF" too. Check the power supply & bias circuits, heater wiring... whatcha gonna do when one of that quad blows up instantly, another redplates & is permanently & grossly mismatched, and another one arcs the heater to the plate? Hope you got a Champ to stick that $60 single 6L6 in. And it's not even NOS! Unlikely, but better to burn up a 50¢ fuse than new set of tubes. Sucks worse if something even more expensive goes! When I hear an amp just "needs new tubes," I always check deeper.

Justin

[Jam]

Thanks guys for the info. What's the best way to test the filter caps? or can you get a reading from the tube socket? The 470 ohm resistors are those the what they call screen resistor? Whats the best way test the bias? Any thing else to check? Thanks

[The Dude]

There are several options and schools of thought on electrolytics in older amps. The best way to check them is with a good cap tester that actually applies voltage to the caps and checks for leakage along with ESR and capacitance. Sans that, you can simply check for AC content on your B+ and bias lines. Or, as many do, you can just replace them if they are aged.

The 470 ohm resistors on the output tube sockets are the screen resistors and you should always check them if you already have the amp apart and especially if you've had a tube fail.

Check your bias voltage at the bias filter cap. It should be just under -60VDC. That will tell you if the cap is good. The bias is fixed in a Bassman 100, so you shouldn't need to adjust it if everything is working correctly.

[Jam]

I tested the 470 ohm resistors tested good but I get lost on the location of the different Cap? Where is the bias filter cap at? The caps under the cap pan what are those called ? When I do the testing for the -60VDC is it ok to test the amp with out the output tubes in? Thanks

[Justin Thomas]

Jam,

Schemo is here. Sorry for link only; limited technology here...

Fender Amp Heaven Schematics - Tweed Blackface Brownface Silverface Bassman Champ Deluxe Princeton Super Vibroverb Reissue

Scroll down for Bassman 100. If someone can put in an image, cool.

HTH,

Justin

[Chuck H]

Leave the tubes out of the amp for the testing.