Picked this up on German e-bay a while ago for a song. Had no idea what it was at the time,but as it turns out..this was one serious build.
Reason for not knowing of it...guess i´ll regard myself as excused cause see...this is an amp out of an Ahlborn C5 organ. Built in West-Germany back in the day. From the looks of it by people who knew WTF they were doing.
A couple of EL-84´s in push/pull. A whole armada of ECC-82´s (12AU7s) and a 150C2 stabilizer tube (approx like a modern day n era zener diode).
Remark is the size of the powertransformer. Massive is the name of the game here seing the mere pair of EL-84´s. There´s approx 280VAC between the HT taps,then a pair of heater windings-one for the powertubes and one for the preamp,and in turn all in all three windings that hand me 14VAC a pop.
Then i guess the output transformer is of more normal proportions and in turn there´s a choke in there of approx 4 Henry. All good.
An amp for an organ huh? Rather sturdy one at that. Checked all of the tubes and although they don´t measure like new anymore they´re far off from being used up. IOW good to go there too.
As you might notice there´s a plethora of octal jacks in there too,mainly used as subgroups for routing voltage where it needs to go within the organ.
The OT. Measured that too and it handed me 7500 Ohms primary and 8 Ohms only outbound. Hm. Not gonna use it this time out. Got a whole different plan in mind.
Origins can come in important.
150C2. A voltage stabilizer. New one to me,altho i´ve played around with other voltage stabilizer tube before. Uses a 7pin miniature socket.
Hm. I really don´t know what to say. Just see that lacing... That there is tube porn from the deep end of the pool. That simple. It´s friggin art. ´N yep. "Mustard" caps. Most likely made by Philips back in the day i presume.
The PT. Damn!
Right. Reused the basically never used octals. Uhu. This´ll turn into a quad 6V6 amp. Correct.
Amp sports two tagboards right. The one has seen its fair share of heat. Tried cleaning that out and measured for it being conductive... Sure looks rather bad but..no contact what so ever.
So. Bias. Stock the one side of bias just hits chassis ground. Not so this time out,a full wave bridge it is and two "banks" as far as bias voltage.
Uhu. The new looks of things huh? The new OT is of just shy of 4k primary BTW. Good for bringing the best out of a quad of 6V6´s.
Internals. Most of what´s needed for the powertubes already in place. An issue was that the bias circuit didn´t hand me much more than 34VDC negative and...that´s on the jagged IF i opt to shove B+ much past 400VDC.
As i plan to use JJ´s 6V6´s that might very well become the case. But? HT secondary handed me a mere 280VAC right? That sure as hell won´t suffice to push B+ past 400...
Might be but..i´ve got a number of 14VAC windings too remember. So. I took one of them and stacked to the bias winding and...presto,we now had 52VDC negative.
Good to go and those two 14VAC remaining might very well be that i stack to the HT one for a good 310VAC and that sure WILL push B+ way up there.
KISS. Keep It Simple Stupid. So a regular rectifier bridge for HT it is...