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FDP Forum / Amp Mods, Repairs, and Projects / Tube replacement for Fender '65 DRRI

Contributing Member

South Florida

Oct 17th, 2016 11:02 PM   Edit   Profile  

2 questions:

a.) I was getting a scratchy sound and then loss of volume. I pulled all the tubes and cleaned the sockets. It cleaned up the sound but it just didn't sound right. Then I noticed two tubes dont light up. That means jone of the 6V6 and one of the 12AT7 tubes do not light up. I think all tubes should light and if they don't then it's time to replace. Am I correct?

b.) I read up and it appears there is a lot of opinion Fender ships with cheap tubes and they recommend and upgrade. I'd like opinions. Should I upgrade and can I do that just be popping in new tubes or do I need to have the bias set by a tech?

(This message was last edited by larryguitar19 at 01:20 AM, Oct 18th, 2016)



Oct 18th, 2016 01:58 AM   Edit   Profile  

The degree of visible light emitted by a tube's heaters is not a specified / controlled characteristic. So it will vary.
However, I would expect most any tube to have some visible glow when viewed all around in a dark environment.
The heater's job is to get the cathode up to operational temperature; do the affected tubes get hot to touch?

It's highly beneficial for a tube amp user to have a known good spare tube of each type that their amp uses.
Then when issues emerge, swap in a good tube into each socket at a time and check if the issue has been affected. If not then replace the original tube and move on to the next socket.

(This message was last edited by pdf64 at 04:09 AM, Oct 18th, 2016)

Contributing Member


too many guitars and not enough hands
Oct 18th, 2016 04:19 AM   Edit   Profile  

Now i'm no expert there are plenty on here a lot more knowledgeable than I.

Question 2 if you change power tubes than checking the bias is a good idea.

But, first up If your not sure see a tech. and if you can be there when they go over the amp and ask question

If you want to learn a little bit about amplifiers look at buying a book like the Guitar amplifier handbook.

it wont tell you everything or how to fix things but it may help in understanding how tube amps work, eg. what everything does and how it operates in relation to each other part of the amp

Contributing Member


Oct 18th, 2016 06:19 AM   Edit   Profile  

I would think one dead 6V6 wouldn't produce a sound anywhere near "cleaned up but not right". I believe the DRRI has 2 12AT7s, is the other one more lit? Try swapping them?

Contributing Member

South Florida

Oct 18th, 2016 09:30 AM   Edit   Profile  

As a follow up--

The DRRI has two 6V6GTs. One glows but the other one doesn't. I switched sockets and the 'bad' tube didn't glow in the other socket so I am satisfied it's the tube and not the socket. The
'good' tube has a blue glue. The bad one has nothing.

It also has 2 12 AT7s and I get the same thing. One glows and the other one does glow but barely.

There are also 4 12AX7A. They all glow nice and bright.

So this tells me I have 2 bad tubes. I think they are part of a matched pair so my guess is to replace them as a matched pair and keep the good tube as a spare for emergency.

The diagnosis is the amp 'just doesn't sound right'. That's about all the technical knowledge I have.

I was curious if some of the sponsors above do tube upgrades and if anybody has any recommendations.

I'm not adverse to getting an entire new set if folks think it makes a stock amp sound better. And by that I mean 'more full'. I like the DRRI but it is a bit thin for my taste. I wouldn't mind getting it to growl a bit more.

(This message was last edited by larryguitar19 at 11:34 AM, Oct 18th, 2016)


United States

Oct 18th, 2016 12:30 PM   Edit   Profile  

I had this exact same issue so I'll let you know what happend to me.

My amp would periodically not light up one of the power tubes, and I learned to just "jiggle" the tube until it lit up, which it did. One day my amp just started making a terrible humming noise, turns out two of the filter capacitors in the power supply had burned out. After I brought the amp to my tech and figured out what the problem was, I haven't had a power tube light go out since.

Maybe that might be the issue, but I can tell you I replaced my power tubes and it didn't do anything. That may not be the case for you, but if you do replace the power tubes and the problem persists you may want to bring the amp to a tech to try and sort out the issue.

Also, when one of the power tubes isn't lit up, you will lose clean headroom as the amp is only at half of its power capacity more or less. This also happend to me so I know what you mean by the amp not sounding right. Hope this helps Larry, and hope the issue is a simple fix.



Oct 18th, 2016 12:54 PM   Edit   Profile  

Do the tubes that you suspect as being failed get hot to touch?

Contributing Member

Irishman in Paris

It's just a guitar, not rocket science.
Oct 18th, 2016 12:59 PM   Edit   Profile  

"The 'good' tube has a blue glue. The bad one has nothing."

Blue glow is not indicative of anything good, bad, or otherwise. It's the orange glowing filaments inside the tube you are looking for.

Blue Glow

Contributing Member

American Patriot

I'm on guard these days.
Oct 18th, 2016 01:16 PM   Edit   Profile  

First thing I thought about was what pdf64 brought up above. Heat! Is that tube getting hot?
Try some new 6V6's first.

This seems to be one of the many problems with these "reissue" amps which aren't a reissue of anything at all.

Contributing Member

South Florida

Oct 18th, 2016 09:09 PM   Edit   Profile  

Follow up....

a.) First of all thanks for all the helpful comments.

b.) I checked the 'bad' 6V6 and it was indeed cold. The dim 12AT7 was glowing and hot to the touch so I decided to leave it for now.

c.) So bought a pair of matched 6V6 GTR's for 49.99.

d.) A little Deoxit and insert and the DRRI immediately came back to life. It sounded exactly like I thought it should sound. I'm guessing the tube was bad for awhile which explains why I retired it for awhile.

e.) I studied up a bit and did a continuity test on the heater pins (I think it was 3 and 8) and got nothing on the bad tube and continuity on the good tube. So I'm guessing the tube has broken filament or something.

f.) On the 'blue glow'..yes I know it's not a diagnostic thing. I just noticed that if I had the amp on and hit the standby switch it pulsed with a blue glow which then faded after a bit. I think that's normal.

Contributing Member

Delco, PA

"I'll take a simple C to G
Oct 21st, 2016 08:07 AM   Edit   Profile  

"I like the DRRI but it is a bit thin for my taste. I wouldn't mind getting it to growl a bit more."

Setting the bias a little on the hot side brings these amps to life. IMHO

Iron Man

USA/Frisco Bay

My eyes are blind, but I can see
Oct 26th, 2016 11:57 PM   Edit   Profile  

I just had my GT tubes swapped to a pair of JJ and rebiased the amp to 25mA. The DRRI really sounds much different and better than before. I'd recommend taking out the pair of 6V6GT.

Contributing Member

South Florida

Oct 27th, 2016 09:47 AM   Edit   Profile  

I bought the last pair of GT6V6's at my local GC. It satisfied my initial concern about diagnosing the problem. It was the tubes.

But I also totally agree with the concept of learning about better tubes.

I am actually looking at my TRRI which 'doesn't sound right' and I'm convinced has the same cheap Chinese tubes.

FDP Forum / Amp Mods, Repairs, and Projects / Tube replacement for Fender '65 DRRI

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