65 Blackface Pro -- no nothing

[Tom Phillips]

...I just bought the same fuse that was in their, a 1 amp...

It's a good thing that you mentioned the value of the fuse. That's an important fact in troubleshooting your problem. It will be interesting to learn how this works out.

For others who read this thread it's a good lessen to learn that you should replace the fuse with the specified value marked on the amp rather than the value found installed. I always check the fuse value when I work on an amp. About 10% of the time I find that it is incorrect. Often the fuse is way over value. Because of that I figure that I have a lifetime supply of 10 to 20 Amp fuses and have probably saved quite a few amps from serious future damage. This same principle applies to other parts in the amp. Over the years old amps tend to build up a collection of incorrect replacement parts. Sometimes they even leave the factory that way. A good tech will spot and correct these things as part of the normal repair or restoration process.

Jim - If your rear panel has obscured or missing markings, now is a good time to put a “2 AMP SLO-BLO” label under your fuse holder.

Regards,
Tom

[river251]

Thanks Chuck and Tom. Looks like I will have to do this in the morning. Will let you know. Tom I didn't think to check the amp itself for a fuse value, I'll have a look.

Jim

[Tom Phillips]

Jim,
If your amp is stock you should find marking on the chassis rear panel similar to that shown in the attached photo.
Tom

[Chuck H]

I always check the fuse value when I work on an amp. About 10% of the time I find that it is incorrect. Often the fuse is way over value. Because of that I figure that I have a lifetime supply of 10 to 20 Amp fuses

No joke. My favorite substitution is when you pop the holder and find the old, blown fuse wrapped in aluminum foil!

[madkatb]

I always check the fuse value when I work on an amp. About 10% of the time I find that it is incorrect. Often the fuse is way over value. Because of that I figure that I have a lifetime supply of 10 to 20 Amp fuses .

You're supposed to return the fuse with the amp with strict instructions not to use the fuse again.

[Tom Phillips]

You're supposed to return the fuse with the amp with strict instructions not to use the fuse again.

You know...when I was writing the thought did cross my mind that someone would ask about the left over parts.
The way I do it is this:
Everything that is removed from the amp goes into a parts box dedicated to that specific amp. Even the wire bits etc. This is shown to the customer when they pick up the amp and they have the option to take home anything they want to keep. Anything left behind is then sorted out between trash, electronics recycle bin and keep for later (Which usually means forever or until the next consolidation of stuff I saved.) There are many things that I encourage the owner to abandon I place and which I immediately dispose of. A good example is an intermittent shorting tube that will just cause another round of trouble if if makes its way back into an amp.
Cheers,
Tom

[acorkos]

...if you mean the red jewel light...I think it's been burned out for a while....

replace the bulb, too..it will help you determine if the amp is on w/all the tubes pulled

[madkatb]

I was suggesting that if you returned the fuse you'd probably have to remove it from the fuse holder the NEXT time you had to work on the amp. I've teased several guitar players that they shouldn't be allowed to touch amplifiers...

[river251]

Jim,
If your amp is stock you should find marking on the chassis rear panel similar to that shown in the attached photo.
Tom

Hey, that's my amp.

[river251]

Pull all the tubes.

Done, a pair of Sylvanias, with pretty much getter left. Hope they are OK. And a "Realistic LIFETIME" 5AR4. Says lifetime so that one's good. Wish I'd remembered to bring my TV-7.

Try out my new Harbor Freight $3 DMM. Yep, beeps on the new fuses, not on the old ones.

Then, with the new fuse in place turn the amp on. If the amp stays on, power down.

Flip power to on. No pilot light, doesn't work, and no noise. Tempted to try standby next. But you guys didn't say to do that so I'm scared to.
Assume amp is on, since plugged in and I flipped the power switch to on. Turned it back off after 5 sec. Pulled fuse, still good.

Install the rectifier tube and then turn the amp on.

Done. Rectifier in. Notice looks brand new. Flip the power switch to on. Rectifier tube produces beautiful violet, bright light just for a sec. Flip power off. Pull fuse, no more beeping, so it's blown. So....do I stop here? I have another 5AR4. I think I will wait and bring in my TV-7 tomorrow and check the other one and the one with the light show. My TV-7 is overdue for firing up anyway.

You guys are a genius! Here is a tall, very icy Blue Moon with a big hunk of orange and a triple shot of Maker's Mark on the side for each of you.

Really, thanks. Looks like I may not be lugging this baby to Albuquerque.

So assuming the other 5AR4 tests good, should I just pop it in, put in a new fuse, and hope all's well?

Thanks a bunch.

Jim

[river251]

I am variacing up my TV-7. The other 5AR4 is a Hewlett-Packard Amperex Great Brittain. Looks new; I pulled it from some lab gear. Hopefully can resume this evening....thanks.

Jim

[Chuck H]

And a "Realistic LIFETIME" 5AR4. Says lifetime so that one's good. (and then later) You guys are a genius!

Funny. If you decide to stick around after you finish this project I think you'll fit in here.

Since the rectifier cause the fuse to go without the amp switched out of standby it is probably just the rectifier tube that is wrong at this moment. BUT, do consider my above post regarding service for an amp that age. There would almost certainly be a tonal improvement as well as a reliability improvement.

[river251]

Funny. If you decide to stick around after you finish this project I think you'll fit in here.

Since the rectifier cause the fuse to go without the amp switched out of standby it is probably just the rectifier tube that is wrong at this moment. BUT, do consider my above post regarding service for an amp that age. There would almost certainly be a tonal improvement as well as a reliability improvement.

Heh. Well with 4 old tube amps, and 10 amps total, I'm glad I found this place. I'm amazed that it's possible to find the problem without taking it all apart and hooking it up to all kinds of test gear. And I would never have known you can turn it on without the tubes in it.

I think the TV-7 is about ready. I'll let you know what it says about the tubes. So I'm guessing I should just put a good fuse in, put in the other 5AR4, and do the test again, then with the power tubes, as in your last post. Will report back.

Jim

[pdf64]

As the rectifier flashed / fuse blew immediately on power up, it's likely that the faulty rectifier was the root cause.
If it had taken ~50 seconds to flash, then there may have been cap problems (the schematic shows the reservoir caps being on the rectifier side of the standby switch).
So yes, plug in a good one and hopefully all should be well.
There is a very simple mod which adds silicon diodes to take over from the tube rectifier in case it shorts, thereby keeping the amp running and reducing stress (from fault current) on the power transformer, see http://www.geofex.com/tubeampfaq/TUBEFAQ.htm#ampmods point #8.
The slight downside is that it may not be obvious in use that the tube rectifier has failed, and the VB+ will rise, with the potential to increase static dissipation of the power tubes
Pete

[river251]

Wow, my Pro is back. In the end I was not able to test the blown and replacement 5AR4s. After variacing it up the TV-7 was troublesome; I contacted a guy who services them and I did things wrong so need to go back and attend to that. But based on advice from Chuck and pdf64, I popped a new fuse and the other 5AR4 in ans viola!, she's back. Man and what an indescribably lovely sound with my Mexistrat.

Thanks guys so much. I have never solved a problem with help in a forum like this before. I'm a bit surprised it's possible, but even more happy.

Thanks, I hope you all have a terrific evening. I'm going to crank it up a bit and play some New Mexican blues.

Cheers,
Jim