As some of you know i on occasion basically rape old tube powered PA systems into rocknroll amps. Maybe not the wisest choice of words but...
Up here in Sweden,the cold north,we´ve got a few domestic brands. One of them being Gösta Bäckström. Or..Goesta Baeckstroem for u english speaking folk.
With production focus in the 50´s these amps by any measure are old by now,and there were a few different versions of them.
One of the more widespread versions was the 128C model,which that there in the pic is. A 128C that is.
Now. Be that as it may i guess most of you are familiar with the Swedish brand Hagström (Hagstroem) and it just so happens that,from what it seems,at one point Hagström basically removed the top cover of an 128C and stuffed that into one of their own cabs.
`N see..this is one of those.
A Hagström/Bäckström in short.
Chassis of these things was designed to take a friggin nuclear blast...while the cab in itself,as can be seen,not so much. Made out of particle board no less.
Yep. The cab has certainly seen its fair share of use. No doubt.
Indeed a model 128C.
Sure enough. That Hagström typical "dollar grin" out back.
As i´ve talked the amp over with friends in the trade they´ve basically told me that..uhu,these amps were an official Hagström product,and there indeed are more of them around.
-"Never mind that..."- Uhu. Take a closer look. These old amps normally sported old British made Mullard tubes. Powertubes being EL-34´s.
Buuuuuut...no. A tube is a tube right? So one of them seems to have gone bust and has been replaced with an old 6L6G!
. Well,the rest of them were Mullards at least.Dustbunnies included as well.
What´s more,yup. That there to the right are fuses.
These old amps hands us the true meaning of the word "air castle". About as point to point as they come. In this case,from what it seems,all stock.
So. ESR meter out..checked various vitals,which were all good to go,and then let her rip. Sure enough,the old warhorse was still alive.
Make no mistake. As platforms to modify into something way more usable today these amps are bar none. Quality of the hardparts is top shelf no argument.
Ultra linear build of the powerstage and what not.
Transformation time then. Pulling this off i saw fit to wipe the entire thing clean,leaving the tube sockets and the transformers basically.
Then a turret board and fresh components all over.
Stock these are cathode bias amps and that entailed making a new bias board as i opted to convert to fixed bias instead. A small board and individual trim pots...
That and the add on of fuses. We like fuses. The socket for the rectifier tube in turn (which is a GZ-34) got a couple of "saver diodes" as well and HT AC fuses.
I´ve been asked on occasion how to splice components together and altho a half blurry pic (focus for the love of god!) i hope this at least gives you an idea. Idea here is to keep the legs of them zeners to the highpower resistors no matter what and this is done by installing a small "coil".
One that i make from single strand wire that i straighten and then coil around the shaft of a small jewelers screwdriver or similar. Works wonders and is easy enough to make.
The components and coil are then,of course,filled with solder.
Right.
Please disregard the black wire that´s in there hip-hap as a makeshift ground for the preamp. It´s just to fire the thing up in its new guise.
Well. Approx 470VDC@34mA per powertube tells us that we´re basically all good to go. Twin EL-34´s at that voltage will make for a watt or two no doubt
Given the whole layout a bit of ponder. It´d be nice,IMO,to be able to keep the looks of the faceplate as is but..doubt i´ll get away with that all said and done seing the features i wanna implement.
As you can see one noval yet has been added at the rear of the chassis. This is the ECC-82 intended for the loop.
Ah! The by now ever so important.....!
Sans we´ll lose an EASY 30 watts of outright power! 
Well. If nothing else chassis,faceplate and what not has been cleaned out. Have no issues what so ever with stuff showing signs of wear and tear...dirt however is another matter all together.
´n further progress. This has led me to somewhat of a dilemma. As is heater voltage will hoover around the 6V mark in 240VAC mode of the powertransformer. That IS a tad low and i´d be easy to persuade into clicking that mains voltage knob to 220VAC instead...
Hoooooooowever.. That will make B+ soar past the magic 500VDC mark with all that entails.. Hm.
Altho this could be easily handled with a MOSFET setup to "burn off" power making B+ come in..basically where ever...that said i think i´m going to try the old school way first to try n keep more with the amps age.
Ie; a high power "pulldown" resistor vs ground.
Well. That´s where the amp is at right now. That completely busted "roof" of the cab i´ve done away with and plan to replace that with a regular piece of plywood. We´ll see where that touches down as well.
