Recent Posts

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Tube Amp Building - Tweaks - Repairs / Royal Vocal Amp 90 Mystery

« Last post by AndreH on June 12, 2026, 04:46:22 pm »

I picked up this Royal Vocal Amp 90 with a 2 x 12 Elk cab for the absolute bargain of $240 on Facebook Marketplace.

I've been unable to find any information on this amp online.

There is quite a bit of hum as well as crackling on some of the inputs, so I'll probably re-cap the filter and coupling capacitors.

The output stage is a classic EL34 push-pull.

The input stage is something I haven't seen before.

There are 6 12AX7's, one for each channel as well as a phase inverter feeding the power stage.

I can see someone has been in here before and made a mess of the spring reverb wiring amongst other things.
What's new to me, is the addition of an AC126 Germanium PNP Transistor for each input channel, first time I've seen them in the wild, had to Google the specs.

Has anyone come across one of these amps? 

Any information, schematics, clues would be greatly appreciated.

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Tube Amp Building - Tweaks - Repairs / Re: Any tips for taming a wild 5E3?

« Last post by bmccowan on June 12, 2026, 03:47:39 pm »

Just mentioning a couple of other options.
 - Since it's cathode biased, a simple VVR is an option. I think Trinity amps still sells a board. I've done it a few times and it works well, although if you turn it down really low the amp loses character.
 - A cheap attenuator. In a weak bourbon fueled moment I ordered a Bugera. But it actually works quite well.
Both options are argued about - just like everything in tube amps!

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Tube Amp Building - Tweaks - Repairs / Re: Princeton Reverb circuit refinements

« Last post by dogburn on June 12, 2026, 02:59:50 pm »

anyone ever added treble and bass controls for the reverb?

I've never heard of anyone adding that level of tone control to a reverb circuit in an amp or outboard unit. The most I know of is the single tone control in the Fender 6G15, which I suppose you could get close to by adding it in before the reverb mix pot.

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Other Topics / Re: Meme of the day

« Last post by shooter on June 12, 2026, 02:25:30 pm »

...

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Tube Amp Building - Tweaks - Repairs / Re: Princeton Reverb circuit refinements

« Last post by johnfromcyrene on June 12, 2026, 12:46:45 pm »

anyone ever added treble and bass controls for the reverb?

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Tube Amp Building - Tweaks - Repairs / Re: Safe to power an amp with a home backup battery?

« Last post by JPK on June 12, 2026, 10:01:14 am »

I've run my amp on my ECO Flow Delta Pro 3 backup system. Worked fine.

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Tube Amp Building - Tweaks - Repairs / Re: Princeton Reverb circuit refinements

« Last post by tristanc on June 12, 2026, 06:48:17 am »

I don't know what the cause of the "raspy" distortion might be, and I do hear some beating in the overtones. I think you're right to go after it.

Having worked with this circuit several times, my personal approach would be to scope your signal through the path to see where your problem originates.  This approach can take some time, but it does work.

Thanks - would you use a sine wave (or triangle?) to spot the extra ‘note’? Any ideas what that might look like on the trace?

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Tube Amp Building - Tweaks - Repairs / Re: First amp build

« Last post by Mongrel714 on June 11, 2026, 11:36:13 pm »

Here we go!

Just dis regard the fuses till we figure out which way to go!

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Tube Amp Building - Tweaks - Repairs / Re: First amp build

« Last post by Mongrel714 on June 11, 2026, 10:33:44 pm »

Ok I have studied these all day and I do see what you mean, In the fuse page I was sent too it said better to fuse on the AC side than the DC side, After diodes is DC?? is that correct? and it talks about fusing both leads, I have not seen one schematic with that fusing, I see the positive about it, but is it really a must or is it ok to just use the HT fuse already on the amp? the way you and others have it wired up? Thanks guys!

I was away for a few days then,

Yes, good to fuse the HT on the AC side, the diodes are the point where the AC is rectified to DC, in the case of the two layouts from further up the page, the rectifier is a two phase type,

Some manufacturers put the HT fuse in the centre tap of the HT winding, I have a few old amps with that fusing and never had a problem, and some Marshalls do it after the rectifier, so you will see two fuse holders on the rear, one for Primary and one for Secondary, but as mentioned on Merlin's Valvewizard site there are some faults which can still leave current flowing even if that centre tap fuse blows, so ideally on a "two phase" rectifier two fuses, one for each leg of the HT, just help protect the transformer a bit more...

Has the "Triode Electronics" layout above been edited, it looks like the two HT fuses have been added, along with another after the rectifier, so there is 4 altogether, also I cannot see the component legs on the board, feels like I'm going colour blind, are the component legs just a slightly darker shade of red

If the amp is well built, setup and running well you would be fine with the "old" style or the two fuse way, as long as you don't put bacofoil in those fuse holders ever again

[I bought an old Sound City once, poor thing used to run so hot, 6x EL34's in there so I just assumed it was that at first, but then I found a Kitkat wrapper in the fuse holder, there was so much jammed in there I bet it would have done more than 10 amps through it before it burned out, it was like solid metal in the holder...]

Hey rontone, Thanks for the answer, I feel a little less in the dark now!! Yes, I put the two fuses before the rectifier just to see if that was the wat to go, and ya, the lines on the circuit board are darker red, didnt notice that, I will fix that and re post the original, and no worries, no more foil! that was my younger and dumber days!! Thanks so much 

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Tube Amp Building - Tweaks - Repairs / Re: panoverb

« Last post by DummyLoad on June 11, 2026, 08:29:48 pm »

Two amps? I has "stereo function for tremelo and reverb" so would that seems like that's the case.

--Pete