Unfixable B15?

You have to wonder why the tech can't provide a cost effective solution. I suspect that they are too busy to take this on.

The PCB may be badly damaged. Even with damaged traces, a piggyback turret board over that section of the board is one way to go.

Below is a 1973 B-15 circuit board courtsey of sjrash, Scot. It's one sided, a pretty basic board.
If there isn’t one on the tray, here is a schematic: https://www.talkbass.com/attachments/ampeg_nf_1968_ii-pdf.830489/

 

When the modifications are done poorly, or not documented, many professional techs won't waste their time and your money on s repair that may be impossible to do correctly. It's just not worth the hassle, and the likelihood that it will be unreliable and come back to bite him in the ass.

I totally understand where he is coming from. Too many unknowns, and too much time required to sort out what may have been done. To do it right likely costs more than the amp is worth.

 

OP, sorry to hear about this.

Is a re-build something you would consider? If all the major components are still there (orig tranny, chassis, ps, pots, sockets etc) you may be in a position to ask if he can strip it and clone a new build. This obviously will cost a bit, but you do already have the most expensive and/or hardest to source parts. This is of course assuming none of the important parts fell victim to the mod failure.

Of course you could source an unmolested one that is DOA or a bit rough and see about him using the best of both to make one good one.

I may also be way off with this. Although they aren't super rare, it sucks to hear about another one gone forever.

Good luck.

 

In your situation, there is no, "what's the worst that can happen". You can absolutely tackle this as a project yourself so long as you have some solid electrical fundamentals, safety stuff being first and foremost.

This is a gross generalization of the knowledge needed, but all you're doing at this point is copying the schematic with wires and components of the correct values (and hopefully quality materials).

It is imperative that you can read the bands on a resistor, understand the values and polarity of diodes, capacitors, transistors, read schematics, etc.

You don't have to be an engineer, but it does take a healthy dose of knowledge, time, and money.

What's the amp worth to you?

Keep in mind, i'm just saying things like needing knowledge. I also have some college background in electronics and several expensive books on the subject. Sometimes the correct amount of knowledge to do the repair can easily cost more than the repair itself.

 

The de-modding, or at least deconvoluting the mods without a road map, will take time, and time is money. I could understand the tech being hesitant to address those issues. Outright saying it's unfixable I wouldn't agree with, but a budget busting repair bill I could certainly see.

Replacing the transformer is pretty straightforward and the old B15Ns in general have a propensity towards wearing them out as they age with exactly the symptoms you describe here. Repro transformers pre-potted are available but cost a decent amount.

 

I would get the amp back, take a pic of the insides and post it here.
Those amps aren't that complicated and I'm not really sure what could be done mod wise to make it completely irreversible.
Unless traces were cut/jumpered.
I'm sure it can be fixed and it may just be that tech doesn't want to work on things that take extra time.....

 

Normally, I would agree (I just took apart a piece of gear I recieved yesterday to do a mod a couple hours after it arrived), but there can be a point where things have gone too far. A co-worker once asked me to help him redo an old tube amp he had. I was gung ho, anticpating a good chalenge, until....I saw it. It was so hacked to bits, that, honestly, I would have feared for my own safety just working on the thing, and I couldn't in good consciense envision turning that thing back out into the world, with a human wired to it.

Hopefully your amp isn't that far gone - I'd try another tech if I were you - a second opinion as it were.

 

As long as you can get parts it can be fixed.
How much time, trouble and expense is another issue.

 

I'll take that piece of junk off your hands to save you the trouble of recycling and e-wasting it...would a six-pack of your favorite brew be about right?

Seriously, sorry to hear about the problem and good luck with resolving it. Bob

 

If you like the pre-amp part, maybe just ask him to mod it to use it just as a pre-amp.

 

I agree with Agedhorse, but I'm thinking here that if the tech was smart enough to notice modifications, then he should be able to trouble shoot why the amp failed. and repair the problem without getting into any modifications. I mean the amp was in running condition. You just didnt find it in the trash and asked him to get it running. Give it the sniff test, maybe a resistor or capacitor must have burned out or failed that can be replaced. Unless the whole circuit board was fried or a bad transformer..either way,. I'll give you two six packs of your favorite beer for it.

 

The challenge techs face is the possible consequences that modifications may have been involved with the failure, or that unidentified modifications may cause another or different failure in the future. There is nothing worse than putting the time into fixing an amp only to find additional issues caused by previously unidentified modifications.

The alternative is for the tech to not warranty the repair, but IME this causes more bad will issues than just walking away from it.

 

And regardless of pre-repair conversations. a failed repair can and will result in negative posts on ever web forum remotely related to any sort of audio. Not saying this about the OP, but most people forget the agreement as soon as the product lets out a poof of smoke and the tech won't fix it for free.

 

Unfixable B15? There ain’t no such thing! They were designed to be easily fixable.

 

Until some hack gets into it and makes it uneconomical to repair. Why spend $000 fixing something that you can buy used in unmolested condition for $700 (as an example).

I see this all too often, an otherwise inexpensive, simple repair f**ked all to hell by a hack tech or hobbiest resulting in a paperweight.

 

I agree Andy but, cost aside, any B15 can be repaired even if it ends ups as a labour of love.

 

It's the old adage:
Feasible, yes. Economical, no.

 

Well, yeah, ANYTHING can be fixed... I could even lay out a new PCB, custom wind a transformer, fabricate a new chassis... I could even build a brand new reproduction from scratch replacing every messed up component. I think there is a not so fine line between what's reasonable and what is not.