Supro Royale -- fading sound

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Tafarel
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Supro Royale -- fading sound

Post by Tafarel » Thu Dec 01, 2022 2:07 pm

I was playing this amp last night with the volume about half way up. It sounded full and and honestly as good as it ever has. However, after about ten minutes of playing the volume started to drop until it was barely above a whisper. I thought maybe it was a cable gone bad, so I unplugged from the board and plugged directly into the amp -- same lack of volume. I changed cables and plugged in and it was still just as weak.

Failing tube?

It has 5881s in the power section, which is a milspec tube -- or at least is supposed be more robust than a 6L6.

Could it be a preamp tube?

I've never had quite this situation before -- in the past things either worked or they didn't. Ideas?
"I'm nostalgic for conversations I had yesterday. I've begun reminiscing events before they even occur. I'm reminiscing this right now. I can't go to the bar because I've already looked back on it in my memory, and I didn't have a good time."

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Re: Supro Royale -- fading sound

Post by Nudger » Sat Dec 03, 2022 12:31 pm

Tafarel wrote:
Thu Dec 01, 2022 2:07 pm
I was playing this amp last night with the volume about half way up. It sounded full and and honestly as good as it ever has. However, after about ten minutes of playing the volume started to drop until it was barely above a whisper. I thought maybe it was a cable gone bad, so I unplugged from the board and plugged directly into the amp -- same lack of volume. I changed cables and plugged in and it was still just as weak.

Failing tube?

It has 5881s in the power section, which is a milspec tube -- or at least is supposed be more robust than a 6L6.

Could it be a preamp tube?

I've never had quite this situation before -- in the past things either worked or they didn't. Ideas?
Have you got any good power tubes lying about?
Reminds me of a prob with my Twin Reverb reish that I run on 2X 6l6s (I think orig fender tubes).. With mine the vol drop wasnt gradual, Just dropped out.
When I say out.. you could just about hear it? As if some one a couple of streets away was playing fuzz guitar.
Then it would just come back to life?!?
Rolled all the preamp tubes with no change.
I touched one of the Power tubes and it was cold? I had an old 5881 Lying about so bunged it in and its been fine.

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Re: Supro Royale -- fading sound

Post by Tafarel » Sat Dec 03, 2022 7:13 pm

The sound was full and powerful and it just slowly rolled down until, as you hinted, it sounded like someone playing fuzz guitar down the block.

Unfortunately, I don't have any 5881s laying around atm. 6L6s aplenty, but I am not sure how this amp is biased. I will check to see if one of the tubes is cold next time I start it up. It's not the easiest amp to change tubes in -- one has to take off the back and kind of blindly find the notch for the octal tubes when putting them (I think, as I've never replaced the tubes in this yet.).

I have plenty of preamp tubes, so I will experiment with them, but they probably aren't the problem.
"I'm nostalgic for conversations I had yesterday. I've begun reminiscing events before they even occur. I'm reminiscing this right now. I can't go to the bar because I've already looked back on it in my memory, and I didn't have a good time."

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Re: Supro Royale -- fading sound

Post by JSett » Sat Dec 03, 2022 11:22 pm

Tafarel wrote:
Sat Dec 03, 2022 7:13 pm
The sound was full and powerful and it just slowly rolled down until, as you hinted, it sounded like someone playing fuzz guitar down the block.
Power tube(s) almost certainly. Classic telltale symptoms.
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Re: Supro Royale -- fading sound

Post by Tafarel » Mon Dec 05, 2022 6:33 am

I picked up a pair Ruby Tubes 5581s (the only ones available here) and swapped them into the amp, plugged in and played for a few minutes, and...

the same thing happened, FFS.

So, I guess I will go swap the preamp and phase inverter tubes one by one and see if that fixes the problem. It's just such a PITA with this amp because the back has to be removed to swap tubes, and the speaker lead is too short to perform this without putting the back on the amp.

This is just a backup amp for me, but we have a bunch of gigs coming up throughout the next month and I sort of need this for peace of mind.
"I'm nostalgic for conversations I had yesterday. I've begun reminiscing events before they even occur. I'm reminiscing this right now. I can't go to the bar because I've already looked back on it in my memory, and I didn't have a good time."

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Re: Supro Royale -- fading sound

Post by panoramic » Tue Jan 10, 2023 7:07 am

Tafarel wrote:
Mon Dec 05, 2022 6:33 am
I picked up a pair Ruby Tubes 5581s (the only ones available here) and swapped them into the amp, plugged in and played for a few minutes, and...

the same thing happened, FFS.

So, I guess I will go swap the preamp and phase inverter tubes one by one and see if that fixes the problem. It's just such a PITA with this amp because the back has to be removed to swap tubes, and the speaker lead is too short to perform this without putting the back on the amp.

This is just a backup amp for me, but we have a bunch of gigs coming up throughout the next month and I sort of need this for peace of mind.
might be a resistor, my bandmaster head was doing this a while back.
I used to be cool, now I just complain about prices.

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Re: Supro Royale -- fading sound

Post by Tafarel » Tue Jan 10, 2023 8:37 am

panoramic wrote:
Tue Jan 10, 2023 7:07 am
Tafarel wrote:
Mon Dec 05, 2022 6:33 am
I picked up a pair Ruby Tubes 5581s (the only ones available here) and swapped them into the amp, plugged in and played for a few minutes, and...

the same thing happened, FFS.

So, I guess I will go swap the preamp and phase inverter tubes one by one and see if that fixes the problem. It's just such a PITA with this amp because the back has to be removed to swap tubes, and the speaker lead is too short to perform this without putting the back on the amp.

This is just a backup amp for me, but we have a bunch of gigs coming up throughout the next month and I sort of need this for peace of mind.
might be a resistor, my bandmaster head was doing this a while back.
Thanks for this. It has been on the back burner for awhile now because I have been mystified by this -- I will explore this avenue.
"I'm nostalgic for conversations I had yesterday. I've begun reminiscing events before they even occur. I'm reminiscing this right now. I can't go to the bar because I've already looked back on it in my memory, and I didn't have a good time."

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Re: Supro Royale -- fading sound

Post by OffYourFace » Tue Jan 10, 2023 6:17 pm

So not a preamp tube? Does it have a tube rectifier?

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Re: Supro Royale -- fading sound

Post by Tafarel » Wed Jan 11, 2023 5:50 am

OffYourFace wrote:
Tue Jan 10, 2023 6:17 pm
So not a preamp tube? Does it have a tube rectifier?
No, not a preamp tube. I don't believe it's tube rectified, either, and there is scant little information on rectification for this amplifier.

Looking under the hood, there are only two big bottles -- 5881 tubes -- 3 x 12AX7, 1 x 12AT7, 1 x 12DW7. I am not quite certain what the 12DW7 does, and am unfamiliar with it. It looks just like a 12AX7, so I assume it is not a rectifier tube.

I went through the tubes one by one -- other than the 12DW7 -- and the ghostly fade remains. Flummoxed.
"I'm nostalgic for conversations I had yesterday. I've begun reminiscing events before they even occur. I'm reminiscing this right now. I can't go to the bar because I've already looked back on it in my memory, and I didn't have a good time."

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Re: Supro Royale -- fading sound

Post by OffYourFace » Wed Jan 11, 2023 7:49 am

12Dw7 is either the driver for the reverb ckt or FX Loop.
The info is vague. Basically it’s like two tubes in one; one half is a 12au7 and the other half is a 12ax7.

Pull it out and see if you lose your reverb when you turn it back on. If not then it’s for the FX loop.

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Re: Supro Royale -- fading sound

Post by Tafarel » Wed Jan 11, 2023 8:57 am

OffYourFace wrote:
Wed Jan 11, 2023 7:49 am
12Dw7 is either the driver for the reverb ckt or FX Loop.
The info is vague. Basically it’s like two tubes in one; one half is a 12au7 and the other half is a 12ax7.

Pull it out and see if you lose your reverb when you turn it back on. If not then it’s for the FX loop.
I will give that a try this evening. Thanks for that!
"I'm nostalgic for conversations I had yesterday. I've begun reminiscing events before they even occur. I'm reminiscing this right now. I can't go to the bar because I've already looked back on it in my memory, and I didn't have a good time."

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Re: Supro Royale -- fading sound

Post by Tafarel » Thu Jan 12, 2023 6:39 am

So... the 12dw7 drives the reverb tank, I believe. I removed it and there was no reverb, but the sound also changed somewhat, too. Its use is still kind of a mystery.

I think at this point I am going to take it to a local amp repair. After i get it back I will likely put it up for sale. This amp is driving me nuts. I've had reissue Supro Thunderbolts and Dual-Tones, but this amp doesn't live up to either of those, which were rock solid and had character-full tone. I know it's a small sample size, but its rather anodyne sound is fine only if you run pedals in front of it -- which I do. The JHS Charlie Brown is always on, in this case, so I can get plexi tones out of it.

I know it's a small sample size, but I doubt I would buy another one even if guaranteed to be 100% reliable.
"I'm nostalgic for conversations I had yesterday. I've begun reminiscing events before they even occur. I'm reminiscing this right now. I can't go to the bar because I've already looked back on it in my memory, and I didn't have a good time."

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