1964 Bassman Head - return or sell here?

jimmyguitar

Hi guys and gals. I recently purchased an original blackface bassman head with fitted flightcase on eBay which was described as in full working order and recently serviced. I took it to my amp tech to give it a health check and he says there's quite a bit of work to do to make it good. 
https://www.ebay.co.uk/itm/232217215975
The replaced transformer is fitted poorly and the chassis is rusty along with a burn mark from a hot valve on the power cable. I think this is all fairly easy stuff for an experienced ampaholic but I don't want to spend any more on it and seller had accepted a return.
https://i.imgur.com/Dv5Kehe.jpg
But here's the thing... it cost me £490 inc P&P which was a good price. Does anyone here want to buy it to save me the hassle of an eBay return? Seems like a great deal if you know what you're doing with amps. It does work and sounds great but I can't afford to spend more on it to make it safe.

ICBM

What's going on under that metal plate on the OT feet? Is that a re-replacement transformer with the plate covering a hole in the chassis from a previous bodge replacement? If so, send it back - a hacked chassis can never really be put right.

The rest of it is standard for an amp this age and nothing much to worry about or hard to fix.

jimmyguitar

ICBM said:

What's going on under that metal plate on the OT feet? Is that a re-replacement transformer with the plate covering a hole in the chassis from a previous bodge replacement? If so, send it back - a hacked chassis can never really be put right.

The rest of it is standard for an amp this age and nothing much to worry about or hard to fix.

I think so yes, I only have the amp report pics to go by as I took it straight to him. Should there just be a wire hole there? I'll look when I get it back.

ecc83

From pictures I can find that transformer is mounted 90 dgrs wrongly from the optimum hum "bucking" position and therefore smacks of a numpty fitter. (and WTF not make a proper adaptor plate?) . It also looks to have a bigger core than the pics I find and therefore is likely to be of the wrong ratio and the amp will not sound like the original, could even bugger valves or/and itself.

Lot of money for a kludge IMHO!

Dave.

ESchap

The OT is the wrong shape for that amp, it should be much longer and utilise the screw holes occupied by the added plate, i.e.  the correct transformer is the width of the doghouse.  If there is no hole cut in the chassis it could be fixed by getting a transformer of the right spec. for the amp.

jpfamps

ecc83 said:

From pictures I can find that transformer is mounted 90 dgrs wrongly from the optimum hum "bucking" position and therefore smacks of a numpty fitter. (and WTF not make a proper adaptor plate?) . It also looks to have a bigger core than the pics I find and therefore is likely to be of the wrong ratio and the amp will not sound like the original, could even bugger valves or/and itself.

Lot of money for a kludge IMHO!

Dave.

Orientation of the OT is fine re hum as the PT is a lay down.

TheMarlin

What's the circuit? AA865, AB165? Some
64's were still 6G6B, but this looks blackface. 

jpfamps

I'd probably send it back if I could, although I guess they would argue that the transformer change was mentioned in the description.

Transformers are the single most expensive items in amps, so any repair requiring a new transformer is likely to be expensive.

The real killer would be if the chassis has been hacked so the correct repro OT can't now be fitted.

The orignal BF Bassman only had a 4 ohm out, so it;s likely that the OT was killed by running the amp into a 16 ohm cab.

I've often seen Fender Bassman with replaced OT where the secondary is whatever the replacement has rather than any attempt to get it "correct!

The Amp Hospital are in my experience very pricey, so you may be able to find a cheaper quote for the work elsewhere.

DJH83004

I think it is worth taking the plate off, since it looks like it is just held with a couple of self tappers, if the chassis has not been butched, the TX may have been changed to give the user multi-tappings for more speaker flexibility. Don't think the mains cable or 'aged components' are a major issues, but it may well need a full cap job (shame he didn't photo under the cap cover), and a few carbon comp resistors and maybe a noisy pot.  

John_A

Although it mentioned a 'new' transformer in the listing the fact it's not the correct one should be enough for ebay to side with the buyer and authorise a return

jimmyguitar

John_A said:

Although it mentioned a 'new' transformer in the listing the fact it's not the correct one should be enough for ebay to side with the buyer and authorise a return

Yes, I've had my return approved and will send it back tomorrow unless anyone here wants it for what I paid. Need to collect it from tech still, I'll put up some pics when I get it back!

clarkefan

jpfamps said:

The orignal BF Bassman only had a 4 ohm out, so it;s likely that the OT was killed by running the amp into a 16 ohm cab.

That's interesting, I thought that was safe, it was the other way round that was dicey, 16 ohm amp into a 4 ohm cab?

ICBM

clarkefan said:

That's interesting, I thought that was safe, it was the other way round that was dicey, 16 ohm amp into a 4 ohm cab?

No - for a valve amp, running into too high an impedance is more dangerous, because very high voltages get developed in the output transformer which can arc through the wire insulation. It will usually self-limit itself with too low a load since the power transfer falls as you get further away from the matching impedance and so not do itself any harm, although it can be hard on the valves. Some valve amps even have a switch in the speaker jack to deliberately short the output in the event of no cabinet being connected, because this is safer than having no load.

Solid-state amps don't have an OT (usually) so the danger is from excessive current being drawn through the power transistors, which is why they must not be run into a lower impedance than the rated minimum, or into a short which will kill them very quickly.

So the rules are almost opposite - most valve amps will safely handle a load between half and double the matching impedance, but lower is safer than higher; most solid-state amps will handle any load above the minimum (there are a few exceptions but they're very rare).

Older Fender amps are one of the ones with a shorting switch in the speaker jack, and are generally very tolerant of mismatched impedance, but as jpfamps says, running into a 16-ohm cab (typically an old Marshall 4x12") is one of the few ways to risk damaging them.

clarkefan

Great explanation,  @ICBM , thank you

jimmyguitar

Hi guys, a quick update as I now have the amp back in my possession. Here are some pics. I missed the deadline to return it to the seller so I've decided to restore it. Looks like the chassis wasn't hacked and the gut shots show what looks like original caps and wiring. Any experts care to examine? @ICBM ;;;
@jpfamps  @DJH83004
https://i.imgur.com/fWXq39p.jpg
https://i.imgur.com/gLpdPkQ.jpg
https://i.imgur.com/4c2iUZe.jpg
https://i.imgur.com/YeiAd4w.jpg
https://i.imgur.com/vhFN4Y8.jpg
https://i.imgur.com/ozCTwGv.jpg

ICBM

It doesn't look too bad, although it would be a good idea to remove the OT and confirm nothing nasty is hiding under that odd plate. The choke has been changed too, and the chassis may have been drilled - I think the original hole is under the blue and brown wires in the bottom pic - that's not a big deal though. So to restore it you need a proper OT and a choke.

The good news is that the bias filter cap has been replaced, so there's a reasonable chance the others have been - have a look under the metal cover. The dual cathode caps are original and might be best replaced, although if there's no evidence of leakage it's not essential usually. The screen resistors have also been changed - technically for slightly the wrong value, although it doesn't matter - and one has then been overheated again, so if it was me I would probably replace both with 5W wirewounds (470-ohm).

Also check that the voltage selector has been hardwired for 240V (I can't quite see clearly enough) and do so if it hasn't.

jimmyguitar

ICBM said:

It doesn't look too bad, although it would be a good idea to remove the OT and confirm nothing nasty is hiding under that odd plate. The choke has been changed too, and the chassis may have been drilled - I think the original hole is under the blue and brown wires in the bottom pic - that's not a big deal though. So to restore it you need a proper OT and a choke.

The good news is that the bias filter cap has been replaced, so there's a reasonable chance the others have been - have a look under the metal cover. The screen resistors have also been changed - technically for slightly the wrong value, although it doesn't matter - and one has then been overheated again, so if it was me I would probably replace both with 5W wirewounds (470-ohm).

Also check that the voltage selector has been hardwired for 240V (I can't quite see clearly enough) and do so if it hasn't.

Can I send it to you for the work? 

jimmyguitar

And thanks btw!

ICBM

If you're in Ascot I'd probably recommend simply taking it to @jpfamps in London, or someone else more local if you know someone good. I'm not really keen on sending things by courier if it can be avoided...

jimmyguitar

ICBM said:

If you're in Ascot I'd probably recommend simply taking it to @jpfamps in London, or someone else more local if you know someone good. I'm not really keen on sending things by courier if it can be avoided...

Ok great I'll try @jpfamps thanks!

jpfamps

Thanks for the recommendations.

I'm away until the 11th May, so drop a line when I get back if you want us look at the amp.

There is a good choice of after market reproduction output transformers and chokes.