GM36 output transformer replacement

Hello.
New guy here.

There`s an ad in my local Craigslist for a GM36 head and matching HK112 60 watt cab for $500 obo.

In the ad, the poster states that the output transformer needs replaced cause it has blown. (Didn`t say how/what happened for it to blow) He also states that the tubes and boards inside are good per being checked out by an amp tech. The seller has also stated that he has already moved on to another amp and is looking to unload this amp as is.
The possibility of buying a $1K set up for less than half price has me trying to keep my wallet in my back pocket.

I AM a mechanically inclined guy and "relatively decent" with a soldering iron.
IF I pull the trigger on this amp, purchase the transformer and replace it myself, is there any other damage that could have been done in the amp from the output trans blowing? I`ll admit, I`m a tube amp newbie.
I mean, if I fix the amp and end up having to spend some more $$$ to get it going, I`d be better off buying new(er).

I`ve searched around online looking for info or videos on what`s involved in swapping out a transformer in a guitar amp and maybe my "Google-fu" is weak, but I haven`t found anything. I`d think it`d be pretty straight forward.

Anyways, is this something I should pull the trigger on?

Thanks!

is there any other damage that could have been done in the amp from the output trans blowing?

Yes there is!  I don't really see how the tech could guarantee that the amp works all except that blown output tx.  Without fitting another one and running it up anything else is speculation on his part.  The GM36 has the usual TSC system installed to take care of the biasing and monitoring of the output valves.  It also has sensing circuitry to switch the amp over to Silent mode in the event of there not being a load on the output.  That is to prevent a dangerous condition and I would suspect that the owner has allowed the amp to have its output unloaded while in use.  That can cause very high flyback type spikes across the output transformer and output valves which can cause the damage you are talking about.  NEVER EVER EVER run a valve amp with no load unless it has special design considerations to cope with it.  Most don't!  This could also damage components in the TSC circuitry too.  How has the tech checked out all of that?  Has he hooked the amp up to another Tx and run it up?  If so why not just fit a tx and have done with it, the guy is presumably paying for the tech's time anyway.  Or is it that the tech is actually his sister's boyfriend's aunt's postman's next door neighbour who "knows a bit about amps"?  You really can't tell about any of this.

You will also find that H&K will not supply you with an official tx direct to replace.  They only work through accredited repair sites who must make the requests for spares and then do the work.  You could see if you could get an alternative type but that runs the risk of not ending up with the same sounding amp as you started with.  The official transformer is numbered "9580256" by H&K but no spec for it is available.  Technically swapping it out should be easy but unless you know what you are doing it is easy to get something wrong and cause more catastrophic damage than you solve.  It's all a bit of a gamble with your $500 I'm afraid.  Forgive the reference but...  You've got to ask yourself one question. Do I feel lucky? Well, do ya, punk?  

Thanks for the reply bordonbert!

To answer all those questions of who was his tech that looked at the amp and determined it was the transformer and nothing else? I don`t have those answers.

I did stop by a reputable amp tech here in the city where I live and asked his opinion on the matter.
He basically said he doesn`t know until he would actually have the amp in his possession and had a chance to look through it his self.
He did say he`d check it out for me for free though. Seemed like a solid dude.

I`m still on the fence about this. If I do decide to get this amp, I`ll keep you all updated.

Good luck with that decision Cobra, I know it's always difficult to decide when there is a real bargain in front of you. You could get yourself a cracking set up for a very reasonable amount. On the other hand...

Your local tech is being very straight with you and to check it out for free is a kind offer. What he said has confirmed that there is no way to tell whether there is anything else wrong in there, and even so it could still be difficult to tell without the spare Tx. Not all things can just be simply measured with a meter. The H&K amps are most definitely NOT like your bog standard Marshall or Fender. Their design is a Hell of a lot more complex and involved with all sorts of systems in there that normal valve amps just do not have. It is those ancillary areas which could be faulty. And remember, the GM36 has a lot of solid state circuitry around the valves too and that is much easier to damage.

Is the amp located near enough to you for you to maybe leave a deposit on it while you get it checked out by your tech, with an agreement to get your money back if it turns out to be more than just the Tx at fault?

Yeah. The amp is local to me.
I don`t know how "willing" the seller would be as far as just putting down a deposit and "giving" me the amp to check out.
If I was the seller, I`d be leery on a good faith sale unless it was somebody I knew.

I did message H&K through facebook. We`ll see what they say. (If I get a response)