Ahlborn C5


Aug 30, 2014

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...


Aug 30, 2014

4pcs of JJ 6V6.
So let´s kill an urban myth right off the bat. It has been said more times then i care to remember that these are 6L6´s in 6V6 glass online.
Well. In contrast to many i happen to own a rather well calibrated U-Tracer and tell you what...it doesn´t know how to lie so here´s the bottom line.
JJ´s 6V6´s measure as a 6V6. Period.
What we DO know is that JJ´s version will take higher plate voltage than many other 6V6´s. This is true,but they that apart measure as 6V6´s and done deal.


IEC jack. Always a good idea when one can. Point being that amps with a "solid" install of a mains wire should thus always have a mains switch that cuts both phase and zero. What´s more the wire for safety ground shall ALWAYS be longer then the other two cause IF the amp for whatever reason falls over and the mains wire is yanked out of there the absolute LAST thing to let go shall always be safety ground. For apparent reasons i guess.
Not so with an IEC jack tho. The IEC is a good idea as the mains wire will come lose...and is thus a ton safer.
I see many builders that IMO do not put enough afterthought into personal safety. Sry to say. In fact,do whatever you wish n want under the hood as long as electrical (read-personal) safety is analy adhered to.


Aug 30, 2014

Things are coming together. That there output transformer will handle at least 45 watts so...
Checked gearing of it and it´ll be rather spot on for a quad of 6V6´s at 8 Ohm and it turn just a tad low at 16 Ohms.
Can´t win ´em all i guess... :D Only differs a few hundred Ohms vs spec but none the less.


A "feature" of many an old German made amp is that they often have soldersupports on the transformers,chokes and what not.
Something I at least frown upon seing how we regard personal safety these days. Thus the wiring for this choke has be desoldered from said support and extensions for the wiring have been soldered directly to the wires coming off the choke. Shrink sleeved and so forth.
In turn distressed by the mere use of a ty-wrap so the solderjoints are exactly that and nothing else. Rubber grommet where the wires pass through the chassis,of course.


Aug 30, 2014

Right. So i got the thing wired to the point where i fired the powerstage up. All good n dandy i guess,but as anticipated B+ voltage was a tad low seing what i have in mind.
I stacked them two 14VAC windings ontop and that made B+ end up at 420VDC @ 25mA per tube. Perfect...


Speaker jacks. We need speaker jacks. These are Switchcrafts which brings that ground reference for the secondary side of the output transformer is via the chassis.
8 and 16 Ohms does it i´d say.
That..and a couple of fuses for the powertubes heaters. Fuses are good,we like fuses.


Next up was the heater wiring for the preamp. Powertransformer sports two such,why the one for the preamp is a separate one. Glue to keep the wiring in place....


Yep. Worked like a charm that too. Both of the heater windings ended up juuuuuuust a tad high at 6,45VAC,but that is so within realms that it can be disregarded really.


A few hrs later... *LOL*
Not all that far from first fire up.


Aug 30, 2014

Uhu. It DOES get intense. No argument,but trust me when i say that every wire´s there for a purpose. A good one at that. From a simplicity POW i guess we´ve left Kansas a while back. There is a tube or two involved see...
That said i need to tidy that bundle there up a bit,but you get the general idea at least.


So it´s up and running then? Yes,yes it is. However...striiiiiiiiiiiiike two for that there output transformer. I´ve used it once before and wrote the lack of performance to my install,didn´t think more of it.
This time out i measured the "gearing" of it (read above) and that checked out right. Or,at least halfways.
Now. The truth is that the amp hands be a mere 12 watts at wide open throttle and at the rate of the amplitude inbound of the 4pcs of 6V6 is all it needs to be and THEN some.
Amplitude vs the output transformer the same...and still a mere 12 watts.
Ergo. There´s crossfire in there. No two ways about it so a new OT it is. I´ll try and handle that already tomorrow.

Now. That said the rest of the amp works as god intended at first fireup. The rather intricate James Network does what it should as does channel select as does the tube powered loop and what not.
Nah. This´ll turn out as expected.

Just need to replace that damn OT. Before doing that all bets are off.


Aug 30, 2014

Some of them just turn out to have "that". This one does. Magic.
The new output transformer made for all the difference and as is..this is one serious powerhouse since of today. DAMN this thing is wide!
From shimmering cleans to downright mayhem. Just press the footswitch and all hell breaks loose.
You friggin bet! Apart from installing the fresh OT today i tossed a few tweaks at the damn thing and..what can i say.? Bingo. Period.
Volume? You´d better believe it! This is one loud puppy as of today! 4pcs of 6V6 at 400 volts sure deliver.

Soundclip coming up.

Now for the looks of that thing. A faceplate and in turn a cab is needed.


Aug 30, 2014


Headshell in the raw. Now for sanding and staining.
Old customer came in the door...got totally gobsmacked so the amp is sold and isn´t even done yet.


Yeah. ´N then sum...


Aug 30, 2014

All said and done this amp was done,just lacking a faceplate. I opted to go as simple as possible and have to say that...yeah. This´ll melt into the design like nobodys business.
Amp is sold and with the install of that faceplate ready for delivery.

In summary running a quad of 6V6 for an outright power around the 50 watt mark sure ain´t sans merit. Amp has a "coarseness" to it that i for one like. The tonecontrol setup in turn makes for a width normally unpresented and...again..if you´re into rocknroll and can´t find "your" tone in this one chances are that tone doesn´t exist