Valve amp chassis threaded inserts and dead spring reverbs

[pete.young]

Parcelforce Pat has just delivered a lovely old Burman 501 to the residence. Nothing to do with me, it's my eldest son who bought this on fleabay.

It seems to work OK but has a couple of issues:

The top of the chassis is supposed to be bolted to the top of the case. Some of the little threaded inserts which press-fit into the chassis have come loose or fallen out. I can see that at least one has been soldered in place at some point. Are there any better replacements that I should be looking for or do I attempt to re-solder the originals back in place?

Secondly , there's no output from the spring reverb. Assuming that the valve is OK, are there any hints or tips to get this working again?

[Chimike]

Try googling " Rivnut inserts " , see if they'd do it. I use them a lot , sometimes

putting an extra washer underneath.

mike.

[pete.young]

Thanks @Chimike, I'll check it out. I was thinking of maybe opening the holes out to square and putting some captive equipment rack nuts in.

Edit: Actually those look just the job. Thanks for the tip.

Edited March 5, 2020 by pete.young

[andrew_actium]

I would check out Farnell for threaded inserts.

Have you a scope to look at the spring reverb input/output?

The way these work is (referring to fender eg)the reverb i is generally matched in with a small transformer at the input and goes directly to the grid of a valve on the output of the reverb spring transducer where the signal is blended with a parallel clean signal.

It could be the input valve cct, reverb transformer or the reverb or output circuit or the cables connecting the reverb (twisting the plugs gently may resume contact).

Reverb unit is most likely as it is a fairly fragile mechanical assembly and prone to damage.

Easy to find replacements if you have model number

Edited March 8, 2020 by andrew_actium

[pete.young]

An oscilloscope? I don't have one myself but I know a man who does. I would guess it's an Accutronics unit from it's age, but there's nothing visible with it still in situ.

This amp will need to go to a technician anyway for re-biasing and generally checking over - it was supplied with 2 wrong power valves, one Sovtek the other EXH - so much for a matched pair. I'll probably get them to look at it at the same time, although modern effects pedals probably render it redundant.

[andrew_actium]

The tech will find out where the reverb signal disappears and should be a straight forward fix.

The valves sound a bit of a mismatch and you will probably hear a distinct improvement when a correctly biased match pAir are fitted and set up

Best

andrew