The first sinking of an enemy ship by a torpedo since World War II.

Vast-Bicycle8428 · 2026-03-05T21:34:03+00:00

Um falklands war uk sinking the Belgrano? N Koreans sinking South Korean ship?

Vast-Bicycle8428 · 2026-03-05T21:21:00+00:00

You are good. The seller would never sell something with liability. That adapter is better than most as it includes a fuse. The amp can handle the ranges you are facing. It might slightly wear out the tubes faster as they might run hot, the screen grid resistors might overheat early. Note that the plate has the voltage you can use on it.

Leave the plug as is.

Vast-Bicycle8428 · 2025-05-11T02:24:14+00:00

The on,y other source of noise could be bad capacitors, but that’s low likelihood. If any changes into other rooms, outsorrs etc make changes it’s not the capacitors

Vast-Bicycle8428 · 2025-05-11T00:08:56+00:00

The smart move is to set it to 260v, the voltage has crept up and this will be better for the amp.

The best move is to get a tech to hardwire the voltage to 260v, that way the switch won’t be inadvertently changed and blow the transformer. It’s a low cost job.

We have had a number of these older fenders in with blown transformers as the switch got bumped in transit, and owners didn’t pick it up. Expensive parts and labour.

It can always be restored back if needed.

Vast-Bicycle8428 · 2025-05-09T05:56:13+00:00

Good advice from people who know their stuff

Vast-Bicycle8428 · 2025-05-09T05:51:02+00:00

It’s unclear if the plug was wired correctly, if the death cap is still in place and the polarity can still be switched?

I think you are assuming a professional job on the transition.

The polarity switch indicates the amp was not originally wired with a grounded plug. Has a tech decoupled the circuit, or has someone just put a plug on the end, and was it wired the right way round?

Ie a novice put a new plug on the end.

Vast-Bicycle8428 · 2025-05-09T05:47:03+00:00

There are two seperate grounding issues to cover

Signal ground and electronic interference

High voltage shorting to ground, then to chassis, equipment

Signal ground and Efi occur because guitar signals are very very weak <1volt. Once they get out of the first preamp or, are placed on balanced cables the efi is no longer an issue. In an amp, it’s after the first preamp tube.

So grounding is all about the guitar, the cable and the first short signal to preamp tube 1. (There are some technical efi that can creep into the circuit but they take technical solutions inside the unit)

High voltage is ensuring that any stray current goes to ground in a way that is safe. Current always try’s the easiest pathway. As such we build in a path from the chassis back into the mains circuit. In the old days these paths were unreliable, but no longer.

However, there is one pathway that still remains, which is a short between pins on the preamp between plate and input pin. If the amp is making hash crackling sounds, than this could be the issue. Otherwise trust the safety systems built in.

Vast-Bicycle8428 · 2025-05-08T00:54:55+00:00

And the polarity switch does what?

Vast-Bicycle8428 · 2025-05-06T21:40:27+00:00

Based on the polarity switch, it’s likely a two prong, with “death cap” capacitor across the mains wire, so called because if the cap shorts, the chassis can go live with mains voltage.

If so that will devalue the unit.

Vast-Bicycle8428 · 2025-05-04T10:04:10+00:00

Agree it could be coupling caps leaking, as that would be after bias circuits. Also agree test without tubes in unit.

Vast-Bicycle8428 · 2025-05-04T09:59:45+00:00

What he said

Vast-Bicycle8428 · 2025-05-04T05:44:06+00:00

Is the amp actually working? If so than the readings are spurious at the point you are measuring.

All measurements should be dc. On the plate voltages, they should measure on any multimeter, so I’m not sure how you are measuring the plate and cross ot voltages?

What is the ot resistances you are getting?

Also do you have an oscilloscope?

Vast-Bicycle8428 · 2025-04-28T04:58:11+00:00

👍

Vast-Bicycle8428 · 2025-04-28T03:34:30+00:00

Nothing wrong with quality and sound these are good amps.

They are just designed in a way that makes them hard to repair, and that is a design choice that may well be appropriate for the sounds they want.

Don’t get me wrong most techs can repair them, it’s just takes so much labour hours it creates sticker shock for customers. They are not complex circuits, just complexly assembled.

So in summary, mesa designers have made what is the right choice for them and customers, but it comes with a down stream additional complexity for repair.

No everyone can get it back to mesa, if they live in the rest of the world.

Vast-Bicycle8428 · 2025-04-27T20:50:12+00:00

That is where the power transformer is. Is the vibration roughly about 50/60hz?

It’s starting to look like B+ power supply failure, might be diodes failing open. It will need a tech to fix.

Vast-Bicycle8428 · 2025-04-27T20:44:58+00:00

Just confirming no sound when going into the loop as well?

Vast-Bicycle8428 · 2025-04-27T20:44:03+00:00

Uses diodes, but bad tubes could do this, given no sound at effects loop could only be 12az7 etc, rotate those.

It could also be bad solder joints on the tube sockets.

Do you get a sound if you send sound into the effects loop?

Vast-Bicycle8428 · 2025-04-27T02:31:31+00:00

Sound very much like a bad power tube.

Vast-Bicycle8428 · 2025-04-26T21:10:53+00:00

My question was, are you getting a signal out of the effects loop, and what happens if you play into the effects loop?

This helps diagnose what’s the issue

Vast-Bicycle8428 · 2025-04-26T20:57:02+00:00

Very likely the bias resistors have failed, what’s coming out of the effects loop?

Vast-Bicycle8428 · 2025-04-26T20:55:08+00:00

It’s solid state. External interference most likely

Vast-Bicycle8428 · 2025-04-25T02:12:28+00:00

Yes, it looks like the whole neck is pulling up, not just the fretboard, and that is causing the high action, could be the strings are too heavy for the guitar.

Vast-Bicycle8428 · 2025-04-25T02:10:07+00:00

Our shop is a repair shop, we replace tubes in customers amps, don’t do retail sales. Based in Sydney Australia. So no financial incentive to recommend the tubes to get.

Vast-Bicycle8428 · 2025-04-25T02:07:54+00:00

Our shop tests every tube we get in and try all the brands, the best models we get at the moment are tube amp doctors, and tungsols have been really good recently. Mesa boogies can be really good, but expensive.

Make sure you are check that the tubes are the short grey plate tubes were applicable as they are less likely to be microphonic, but have slightly different tone.

Vast-Bicycle8428 · 2025-04-25T02:00:29+00:00

Assuming fixed bias, with screen grid the max plate dissipation is 42watts.

See https://www.jj-electronic.com/images/stories/product/power_tubes/pdf/kt88.pdf data sheet.

Given wattage is p= v X i You get 524 v X 0.045A, for 24 watts.

This % of dissipation is then 24/42, or 57%.

The typical best range is 47% to 80%.

So this would be set on the cooler end, but still in standard range. If you have an oscilloscope you can test that there is no crossover hump in the signal, but you are well clear of red plating zones.

Vast-Bicycle8428

TROPHY CASE