tube amp tune up?

[dg27]

I have a trusty Music Man 100B (100W tube bass head) that I haven't used on a regular basis in several years. I turn it on periodically just to make sure it's OK (it has been). I'm going to need to start using it on a regular basis again.

Today I noticed that the volume pot is pretty crackly. Otherwise it seems OK. I have always used Mesa Boogie 6L6 GC tubes. These have been in there for years. I was going to get new ones, but a guitarist friend who is a tube amp aficionado says that would be a mistake and that unless they're acting up I should leave them as is. (He pointed out the "vintage" (i.e., old) tube are regularly for sale on eBay.)



Is there anything I should do to get this road-ready? Should I have my guitar tech (who services amps) give it a once over to make sure no caps have gone bad?

Anything else to consider?

[LLL]

Re: tube amp tune up?

...

[Boogie Bill]

Re: tube amp tune up?

Did you have it biased for the 6L6s? Most MM use 6CA7s.

Bill

[dg27]

Re: tube amp tune up?

Thanks for the replies.

- Caig Deoxit for the pots

- The big can caps are typically good for a decade (rough estimate and depending on many things); you'll know they're bad when you start
hearing funny overtones coming through the regular tone (they filter out AC IIRC)... or worse, they leak (visual inspection).

There seems to be a high-frequency hiss when the volume is increased.

Note: for tube amps that sit and collect dust, it's good to turn them on now and then to help the can caps stay fresh.

I've been doing that, but not religiously.

Did you have it biased for the 6L6s? Most MM use 6CA7s.

Bill

I'm sure that at the time I replaced the tubes with whatever was in there (and just used Mesa because I'm a big Mesa fan: Mt 1X15 + 2X10 cabs are MB.

I think a once over by my tech is called for...and a new pair of tubes.

[mantis]

Re: tube amp tune up?

It's never a bad idea to change your tubes. Tubes wear out and then start sounding awful.
Get that bad boy into the shop and let a professional give it a once over. It will sound like new afterwards.

[dg27]

Re: tube amp tune up?

It's never a bad idea to change your tubes. Tubes wear out and then start sounding awful.
Get that bad boy into the shop and let a professional give it a once over. It will sound like new afterwards.

Thanks--that was gut feeling too. I've known my tech for ages. He wouldn't do anything that wasn't necessary.

It sounds OK, but only OK. I thought it was noisy.

[dg27]

Re: tube amp tune up?

So my usual tech no longer does amps, but he referred me to the best guy he knows.

Here's what he did:



Boogie Bill: The original tubes were indeed 6L6 GCs, but the head did need to be re-biased.

Got to admit I don't know what most of this means, but the amp sounds better than it ever did.

Thanks for the replies.

[regan]

Re: tube amp tune up?

At a guess:

Secure all grounds = tighten the screws and/or resolder the'ground' to the chassis

clean and retension jacks = clean and tighten input jack speaker jacks line out loop etc

clean and retension tube sockets = clean and tighten tube sockets to chassis

Reflow overheated PCB = where the solder track on the PCB has come away more solder has been applied to replace the damaged solder

Old frayed wiring replaced = replaced any tatty wires

power tube socket reflow connection = resoldered the power tube sockets

Sounds like a retube and general service to me, he's changed your oil, tyres wiper fluid brake fluid, and valeted it nothing major but it seems nothing major (transformers/components changed) appears to have been needed

[dg27]

Re: tube amp tune up?

Thanks for the clarifications. The amp is about 32 years old, so it was time...never had any service whatsoever.

[Chickenwings]

Re: tube amp tune up?

Today I noticed that the volume pot is pretty crackly.

you can probably fix that with some contact cleaner spray

but a guitarist friend who is a tube amp aficionado says that would be a mistake and that unless they're acting up

Tubes are like car tyres. They wear out. There is also the possibility of flats. You can drive in a car with old, balding tyres but it wont handle well.
Get a new set (JJs are excellent for headroom) and keep the old ones as spares.
Tubes in a regularly used amp normally last around a year before starting to lose response. Yours might be ok, but a fresh set can only be a good thing.
I hope your friend is talking about NOS (or new old stock tubes) these are old tubes, but unused - so essentially brand new. Buying old used tubes is equivalent to buying old used tyres.

Re: caps. I had to replace the filter caps in my 1975 musicman because they were leaking. Unless you have done them recently then im sure they are well past their "use by" date (normally 10 years).
Upside of that old musicman is that they are built like tanks inside. Really good gear that should last you a lifetime after a little maintenance.

edit: stupid me i just scrolled to the bottom and skipped the bit where you said you have had it serviced already. All that stuff looks great. I notice he didnt do anything with the filter caps tho, but hopefully he inspected and tested them?

[dg27]

Re: tube amp tune up?

you can probably fix that with some contact cleaner spray

I'll keep this in mind for future reference. Thanks!

Tubes are like car tyres. They wear out. There is also the possibility of flats. You can drive in a car with old, balding tyres but it wont handle well.
Get a new set (JJs are excellent for headroom) and keep the old ones as spares. Tubes in a regularly used amp normally last around a year before starting to lose response. Yours might be ok, but a fresh set can only be a good thing. I hope your friend is talking about NOS (or new old stock tubes) these are old tubes, but unused - so essentially brand new. Buying old used tubes is equivalent to buying old used tyres.

I would estimate that I last changed the tubes (and did not re-bias) about 1995. I saw the JJs he put in, in the boxes: The boxes looked old, but the tubes were definitely new tubes.

Re: caps. I had to replace the filter caps in my 1975 musicman because they were leaking. Unless you have done them recently then im sure they are well past their "use by" date (normally 10 years).I notice he didnt do anything with the filter caps tho, but hopefully he inspected and tested them?

I specifically asked him to check them: They were fine. He said it's part of his normal service.

Upside of that old musicman is that they are built like tanks inside. Really good gear that should last you a lifetime after a little maintenance.

edit: stupid me i just scrolled to the bottom and skipped the bit where you said you have had it serviced already. All that stuff looks great.

I played it the day before I took it in. Aside from the crackly volume pot, there was a very high frequency hum of some sort. Now it sounds better than it ever did.

I toyed with the idea of getting an Ampeg PF350 and scrapping this, but I've always loved this amp. Glad I went this route instead. I use Mesa cabinets; usually only need the 1X15. Love how this setup sounds and even more so now.

Thanks for your input!

[crusty philtrum]

Re: tube amp tune up?

Today I noticed that the volume pot is pretty crackly.

On amps that are seldom used, crackly pots can usually be 'fixed' by simply rotating them back and forth between extremes about twenty times ... you can do it with the amp turned on and usually hear the crackling subside as you work the control knob back and forth. What you are doing is removing accumulated dust from the carbon track and/ or metal wiper contact.

This method is preferable to spraying any kind of fluid into the pot, as fluids usually dry to some kind of sticky surface that simply collects more dust sooner. By all means try a cleaning fluid if the abovementioned method doesn't work, but at that stage I'd be looking at simply replacing the noisy pot with a new unit.

[dg27]

Re: tube amp tune up?

OK--thanks. I'll keep this in mind. When I used it on Sunday I actually did play around with the pot (turning up and down), but something else seemed to be going on: I was getting some really loud pops. I was concerned about killing a speaker, so I decided just to take it in.