Need advice on problem with my new amp please.

[Lend27]

I got a new Fender 1968 Custom Deluxe Reverb (Silverface) amplifier for Christmas.
I love the amp. I was playing it the other day, when the light went out in the panel.
I checked the fuse and it was blown. I replaced the fuse and it blew again.
I removed the power tubes and rectifier tube, and replaced them all with new tubes.
I put in a new fuse and turned the amp on and all was well.
Then I got out my bias probe and found that I could not get a reading from one of the power tubes.
I put the probe on the other power tube and got a reading so I set the bias at 20.2 after checking the
plate voltage which was 413.
I couldn't understand why I could not get a reading from the other power tube,
as I had checked them both in the past.
After doing a bit of research I concluded that when the power tube went, it blwe the fuse and blew the
screen grid resistor for that tube.
So my questions are:

1. Is that something I can do myself? (I can solder)
Note: Although the amp is under warranty, the closest repair center is an hour away.
2. I can play the amp, and both tubes glow slightly. How much would this blown resistor effect the
overall tone of the amp? (Don't notice anything unusual right now in terms of tone).
3. If I wanted to do it myself, what value resistor would I use?

Thanks for any input you guys can provide.

Len

[Leo_Gnardo]

I think your analysis is spot on Len. I haven't had a look in one of this particular model Deluxe but certainly worked on many standard DRRI's. If yours is built similarly, the foil side of the board is what you see when you look inside. Of course, power off, AC line unplugged. Good idea to discharge hi voltage filter caps for your safety before going any further. Easy enough to identify pin 4 of each output tube's socket. The trace leading from pin 4 will meet the screen grid resistor, and it's easy enough to measure them with your ohmmeter. Likely one will measure OK, 470 ohms, the other open. You have the option now of melting solder pads on the bad one, push its leads thru the board, and it will drop off then you can shake it out of the chassis. OR you can leave it right there and simply solder your new resistor onto the pads, on the foil side of the board. I like to remove the bad one then you can poke leads on your new resistor into the holes for a little more stability whilst you solder.

A missing/open screen grid resistor will not affect the way the filament glows at all.

Tone wise, your ability to play loud & clean would be very limited with only one tube working.

Typically we see 470 ohm resistors in Deluxe screen grids. 1 watt minimum, if yours is larger no problem. 5%, good enough, don't need super precision here. Resistor composition? Carbon comp used to be the standard, they would take a lot of abuse but now hard to find. Metal oxide, probably the best modern choice. Carbon film & metal film don't well tolerate the kind of abuse they might find in this application.

Hope this helps!

[Enzo]

This assumes that your ability to solder results in clean joints that look right in place on the amp. You may have a more serious need for warranty repair at a later time, and if they go in and find globs of solder, lifted pads, and other eveidence of low grade work, they may yank your warranty.

Your diagnosis is reasonable, but the first step is not to replace the resistor, it is to get out your meter and verify the resistor is open. We feel silly when we go get a resistor, and replace one on the board, only to find the problem was a burnt open trace an inch away.

[Lend27]

This assumes that your ability to solder results in clean joints that look right in place on the amp. You may have a more serious need for warranty repair at a later time, and if they go in and find globs of solder, lifted pads, and other eveidence of low grade work, they may yank your warranty.

Your diagnosis is reasonable, but the first step is not to replace the resistor, it is to get out your meter and verify the resistor is open. We feel silly when we go get a resistor, and replace one on the board, only to find the problem was a burnt open trace an inch away.

I think, to play it safe, I will take it to an authorized warranty center. Just in case there are any other issues to be resolved.
Thanks guys!

[Enzo]

Call the warranty center, ask if they would be able to inspect the amp and possibly do the repair "while you wait", then go have lunch somewhere for a couple hours. Explain you are asking because of the long drive and would like to avoid two trips if possible.. Worst can happen is they say "no". And be aware they cannot guarantee our distant diagnosis is corect or is all of what is wrong.

If you have never done warranty repairs, they will need a copy of your bill of sale or invoice. If you don;t have one, contact the seller and ask them for a new copy of your "proof of purchase".

[Tom Phillips]

And consider presenting the amp to the warranty center with the original tubes (including the bad one) and the blown fuse. I would leave the power tubes and rectifier uninstalled and just tell them that you took them out and didn't want to risk re-installing the power tubes in different positions and potentially cause further damage to the amp's circuitry.
From what you originally posted I believe that the amp is only about 2 months old and, unless they have changed the warranty terms, the tubes are guaranteed for at least 90 days. You can keep your new tubes as spares. I think that the warranty should cover all costs.

[olddawg]

And consider presenting the amp to the warranty center with the original tubes (including the bad one) and the blown fuse. I would leave the power tubes and rectifier uninstalled and just tell them that you took them out and didn't want to risk re-installing the power tubes in different positions and potentially cause further damage to the amp's circuitry.
From what you originally posted I believe that the amp is only about 2 months old and, unless they have changed the warranty terms, the tubes are guaranteed for at least 90 days. You can keep your new tubes as spares. I think that the warranty should cover all costs.

I would put the original tubes and the original blown fuse back in it and play dumb as a rock. Just say it's under warranty and it died. Do say that you are a working musician and need the amp as soon as possible. If you are lucky they will check it out while you wait. Unfortunately not all repair centers are as friendly and efficient as the guys on this board. But yeah, even if you are a couple of weeks out of parts warrant they should make an accommodation.

[Lend27]

I would put the original tubes and the original blown fuse back in it and play dumb as a rock. Just say it's under warranty and it died. Do say that you are a working musician and need the amp as soon as possible. If you are lucky they will check it out while you wait. Unfortunately not all repair centers are as friendly and efficient as the guys on this board. But yeah, even if you are a couple of weeks out of parts warrant they should make an accommodation.

I brought it to the auth service center, they checked it all out, re-biased it, and all is well.
Thanks for the advice guys

[Richard]

So they gave you same day service? Sweet!

[Lend27]

So they gave you same day service? Sweet!

It was even better than that The amp tech let me watch as he checked out and rebiased the amp. It took all of 30 minutes, and I was on my way home. They were great!
The name of the store is Heyday Music in Asheville NC. What a great place! Lots of vintage guitars too

[Leo_Gnardo]

It was even better than that The amp tech let me watch as he checked out and rebiased the amp. It took all of 30 minutes, and I was on my way home. They were great!
The name of the store is Heyday Music in Asheville NC.

Good to hear Heyday sorted your amp out on the hot foot. In your first post you were getting no current thru one output tube, indicating possibly/probably a bad screen grid resistor. What became of that? Did Heyday replace a resistor or was one of your replacement tubes defective?

[Lend27]

Good to hear Heyday sorted your amp out on the hot foot. In your first post you were getting no current thru one output tube, indicating possibly/probably a bad screen grid resistor. What became of that? Did Heyday replace a resistor or was one of your replacement tubes defective?

Actually, they had no problem getting a reading on both tubes, and no resistor was blown. The tube that blew and took the fuse with it was the rectifier tube. It's playing fine now, and I am able to get a reading from both tubes. I'm happy