65 Blackface Pro -- no nothing

[river251]

My beloved Pro sits in my office. Last time I fired her up, she played wonderfully, a few months ago.

Tonight, I put my Kendrick reverb on top, turned on both, Kendrick lit up just fine, but, no sound, no glow, no nothing from my sweet Pro. Moved the tubes around a little, no help.

Any suggestions on what to try?

Is there a place that will help me understand the schematic?

Thanks,
Sad Jim

[Chuck H]

Did the pilot lamp come on?

[river251]

Thanks for the reply. No, if you mean the red jewel light, it didn't but I think it's been burned out for a while. But I watched and felt the tubes...no glow, no heat. Fuse is fine, and I switched the plug to the one that powered up the reverb ok.

Thanks,

Jim

[Chuck H]

OK. That makes troubleshooting a little harder. Do you have a DMM? Or any kind of ohm meter? I'm thinking that your fuse may be blown. You can test the fuse (if it isn't visibly blown) with a meter. That amp is old. I suspect there may be trouble with the power supply filters and/or the power tubes. Both are wear parts that require occasional replacement. Sort of like tires and oil for your car. One exception being that power supply filters wear out with age whether they are used or not. In fact, low use or long periods of no use makes it worse! If the amp hasn't been serviced by a (caveat = competent) tech, there is a good chance that both require service.

NOTE: There are a frightful many incomeptent techs that don't like to replace original parts in vintage amps until they utterly fail. If your amp guy is such a person, you should stop using them in favor of a shop or tech that focuses on the electronic principals involved in circuit operation. Whether "vintage" parts sound (or sounded) better than modern parts is subjective. And marginalized parts never sound as good as new parts. So if the vintage original parts don't perform to full spec (and certain parts in that amp, if original, absolutely can't) it is only detrimental to keep them in there. I have a special dislike for techs that favor marginalized vintage parts to well chosen replacements. Rant over.

[river251]

OK. That makes troubleshooting a little harder. Do you have a DMM? Or any kind of ohm meter? I'm thinking that your fuse may be blown. You can test the fuse (if it isn't visibly blown) with a meter. That amp is old. I suspect there may be trouble with the power supply filters and/or the power tubes. Both are wear parts that require occasional replacement. Sort of like tires and oil for your car. One exception being that power supply filters wear out with age whether they are used or not. In fact, low use or long periods of no use makes it worse! If the amp hasn't been serviced by a (caveat = competent) tech, there is a good chance that both require service.

NOTE: There are a frightful many incomeptent techs that don't like to replace original parts in vintage amps until they utterly fail. If your amp guy is such a person, you should stop using them in favor of a shop or tech that focuses on the electronic principals involved in circuit operation. Whether "vintage" parts sound (or sounded) better than modern parts is subjective. And marginalized parts never sound as good as new parts. So if the vintage original parts don't perform to full spec (and certain parts in that amp, if original, absolutely can't) it is only detrimental to keep them in there. I have a special dislike for techs that favor marginalized vintage parts to well chosen replacements. Rant over.

I'm with you on the note about servicing.


OK just pulled the fuse again. It's kinda dark in here, but it looked fine the first time, but holding it to the light, the spiral wire looks intact but there are tiny charred droplets around the middle and a definite bit of char on the inside of the glass. Loooks blown, will get my DMM in the morning.

But, then, doesn't it mean something is wrong if it blows?

Jim

[Chuck H]

Yup... Probably a bad power tube or the power supply filters. There's also a chance it could be a bad bias supply. The filters in the bias supply go bad just like the power supply filters. These would be the most common problems associated with a blown fuse and an older amp. Impossible to say for certain without more info.

[river251]

So these problems could happen while it's just sitting, so that it plays fine, then sits, then blows a fuse?

Should I put another fuse in to see what happens, or take it to my tech (who is in Albuquerque 3 hrs away, will be going up there in a couple weeks).

Thanks Chuck.

Jim

[pdf64]

Try another fuse - ensure it's a slow blow / T type.
Suggest you try the procedure in
Vintage valve equipment
this and any time tube gear is being powered up after a few months 'rest', to bring the caps back to service gently.
If fuse blows again, then it's time for the tech.
Pete.

[river251]

Thanks Pete. That procedure scares the heck out of me, given what amp it is. Too precious. I wish I could test it myself. I'm reading up on tube circuits because I also have a tube hifi. But I don't know enough to read a tube amp schematic yet so better not.

I agree, try another T slow blow 1 amp 250v (that's what blew) fuse and if that blows, get it checked out. Fortunately there is a really superb tech in Albuquerque. There is one in El Paso I have never used, which would be fine for a non-special amp like this one. Will be in Albuquerque in a week or two so will take it then.


Jim

[Tom Phillips]

...I agree, try another T slow blow 1 amp 250v (that's what blew)...

Jim,
The specified fuse for a Fender Pro running on 120V mains is 2 Amp. The 250V fuse RATING is correct so don't get confused about that. Install a 2 Amp Slo Blo, 250V fuse. The physical size specification is "3AG" which can be another confusing marking on packaging or in a catalog. It stands for size three, Auto Glass.
Tom

[pdf64]

Yes, 2 amp slow blow.
Don't sweat about the procedure; all it's saying is that even if the fuse doesn't blow, don't get complacent, switch the amp off and give it a few progressively longer 'ON' cycles.
It's quite common for guys to report that they fire up an amp that they haven't used in a while, get playing it because they forgot how good it sounds and then it pops a fuse after 20 minutes.
Pete.

[Bruce / Mission Amps]

Thanks Pete. That procedure scares the heck out of me, given what amp it is. Too precious. I wish I could test it myself. I'm reading up on tube circuits because I also have a tube hifi. But I don't know enough to read a tube amp schematic yet so better not.

I agree, try another T slow blow 1 amp 250v (that's what blew) fuse and if that blows, get it checked out. Fortunately there is a really superb tech in Albuquerque. There is one in El Paso I have never used, which would be fine for a non-special amp like this one. Will be in Albuquerque in a week or two so will take it then.


Jim

WAIT!
PULL THE POWER TUBES AND THE RECTIFIER OUT FIRST!
If it does blow the fuse with no power tubes or rectifier, you can decide if you want to take it somewhere for a repair.

If the new fuse does not blow when you power it back up... you probably have a bad rectifier tube or bad power tubes.
Put only the rectifier tube (GZ34 or 5AR4) back in.... if it blows the fuse, that rectifier tube is bad.
Now install the two power tubes too.
If it blows the fuse when you reinstall the power tubes, then you have at least one really bad power tube.
This should be very simple to do and take you like 15 mins.

[Chuck H]

I didn't cover trouble shooting because the OP doesn't seem too interested in getting into it. But reading your post I did think of another common problem with older amps. Oxide on the sockets or pins for the tubes. If a failed contact causes a bias fault this could also cause the fuse to go. Since it doesn't seem like the amp has had much service, and it's old, I think a trip to a good shop or tech is in order above finding a grossley bad tube and replacing it. At this point the amp should recieve the following service:

replace two prong AC cord with a proper grounded cord (if it hasn't already been done)
clean all non fixed contact points
replace any questionable tubes
replace any electrolytic caps in the amp (that haven't been replaced in the last five years)
check for and replace any badly drifted resistors
reflow any questionable looking solder joints
set bias

This is a pretty standard list for old tube amps. Once it's done the amp should sound like new and provide you with many more years of trouble free operation. But this stuff needs to happen every couple of decades. The bill for such service should run between $200 and $400 depending on how much of the above list requires extra care or parts. This provided there is nothing major wrong with the amp at this time. It's a pretty good deal when you consider the quality of that amp and the cost of a new amp.

It's a little funny that old amps are more economical to maintain and use than old cars. Probably something to do with the facts that cars are needed by everyone and musicians often don't have much money to start with.

[river251]

Thanks much guys. Doing the test with the tubes sounds reasonable. I'll give that a shot. I am happy to troubleshoot if I'm confident I won't hurt the trannies. But knowing nothing it's pretty hard to have any confidence.

I just bought the same fuse that was in their, a 1 amp. If it worked fine all these years, then assuming no problems, it should still work. I'm too impatient to drive back to RS for another $4 package of fuses. Probably cheaper at Autozone anyway.

So just to ease my worried mind, putting the fuse in then putting in the rectifier then the power tubes, while the amp is powered up and on, presents no risk to the transformers?

Thanks y'all.

Jim

[Chuck H]

Pull all the tubes. Then, with the new fuse in place turn the amp on. If the amp stays on, power down. Install the rectifier tube and then turn the amp on. If the fuse doesn't blow flip the standby into the play mode. If the fuse doesn't blow, power down. Install the power tubes and turn the amp on. Wait one minute and flip the standby switch into the play mode. If the amp stays on you just blew the last fuse. Probably because it was old and under rated. You should be as good as you were before the old fuse blew. But you should replace the 1A fuse with the correct rated part. If the amp blows the new fuse at any other step along the way let us know and we will tell you what you can do next. And you can decide again if you want to proceed for yourself.