Hummel,the studio guitar / Soundclip

[Racing]

Yeah.
This time out we´ll be covering a REAL oddball amp. Might be that some of the old farts on here,like me,are familiar with German Klein&Hummel studiogear and what not.
At the time considered some of the finest there was. Well. As it turns out they made a guitar amp too. One. "the studio guitar",and it is odd..from more than one aspect.

I think it´s rather safe to date this amp to 1963. Reason is simple,it was when the newly developed ECC-808 was put in the market and..several German manufacturers jumped the bandwagon. Apart from this Hummel Klemt did too on a rather wide front as did Telefunken (or course),Hohner and several others.

However this amp i believe to mainly have been targeted at the US market and i conclude that from the rather odd choice as far as powertubes,the 7355´s. A tube that can be compared to the way more commonly used 7591.
Amp sports a quad of them and after having fired the thing up today i´d say that 4 of those will hand us just shy the 100 watt mark. Both 7355´s an 7591´s are rated lower,but this at a lower running voltage. Their reference wattage is 18 watts a pop.



The faceplate of this thing is a story in its own. Apart from the rather...different looking dials the word "Hummel" has been cut out in the aluminium and the whole deal is lit from the rear through a piece of green plastic. Different i believe is the right nomer.
Faceplate kind of hands the impression that this is a rather large amp,which is false. It is about the size of the Klemt S-40/BS-40´s approx. IOW around the 19" mark. Weight comes in shy of the 13kg mark



As stated the amp is rather low in profile. That brings that the 7355´s are tilted. This is an issue as newer production 7591´s are way taller. I´ll handle that by fabbing a new piece of sheetmetal that i´ll install the octal sockets to and then countersink the entire deal. No matter the 7591´s will fit the bill just perfect. They´re about deadringers for the 7355´s,just take a tad different negative g1 voltage to establish bias correctly.



From a pure electrical standpoint tho..not all that much new,if you disregard the amps age. Tremolo circuit of it is about a deadringer for what we find in a common Fender Deluxe Reverb.
For better for worse this particular amp has seen a bit of work by Mr Handyman previously why i took to clean that up right off the bat. Wire gauges heavy enough to work for a towline... A very crude rectifier setup for bias voltage and what not.

So. Measured ESR for the various e-lytes and let the thing rip. Didn´t take long for the B+ fuse to go skyhigh...which was the first hit e-lyte saying bye-bye... Replaced that and fired her up again.
Sure enough. Sound. How it sounds? I´ll try and record a clip of the stocker the next couple of days.



In a typical German manner everything in due order. This means that even them trim rings for the dials are bolted in place.. . This beautiful faceplate.. Full of scars tho why i tried taking some rather fine grit emery to it coupled with water and detergent..which seemed to work. IOW..we´ll get that thing back to at least reasonable former glory time permitting.



Pots of it were really worn. Have taken most of them apart as of this writing,cleaning them out and have retensioned them within.

What´s to come of this? I dunno yet TBH. I´m going to keep within the realms of the amp though,seing how scarse it is. If anything i could always just lift the entire,complete,tagboard out of there for safe storage and build it up as i see fit i guess. A few mods are in order though as noted. The 7591´s being of them written in stone,no one uses 7355´s anymore..

..to be continued lads..

[countertext]

*STNDIO GNITAR

[Kent]

Can't wait to hear this one.

[Racing]

Alright. So fabbed this aluminium plate to be able to install the 7591´s. In hindsight,i need to turn the sockets around 180deg. It simply gets to clustered as is,for looks if nothing else. As you can see i added a couple of fuses for the heaters for the powertubes. Preamp ditto is a winding of its own.



In turn an upper plate needs to be installed too. Again for looks. That there simply won´t cut it.
Unbolted the OT as you can see and indeed there´s an extra tap in there. Going to check the windings ratio and see what that hands me. As is i have a feeling that the OT is "one size fits all",like many a Fender amp. That turns ratio reply will tell...



Then again. This amp has been through some in its life. This much is for sure. For some reason there´s a sort of "sag" resistor installed of approx 20 Ohms first thing. Don´t really see any need for that.
First drop resistor in turn is a massive 5k. Again? To what avail? Hoooooowever....



Again. This amp has been through some hard times. No doubt. To the point where parts of that rather heavy duty tagboard has been burned to the ground. Thus i´ve come to inspect the wiring off of the PT and to be honest...it needs to come out and have fresh wiring installed. It´s that simple.
That there injury to the board in turn settles the reasoning as far as keeping it or unbolting the thing as is and saving it for future use...and replace with a fresh turretboard instead.
Further issue is that the chassis has seen some rather heavy duty use too right there rendering that the anodizing is basically black to the color. IOW...soot.

What this brings is that the chassis needs to be wiped completely clean and then cleaned out before the reinstall of the transformers and what not. In turn fresh boards all over. Enough of this trying to beat life into a dead horse.

All said and done though,how does it work with the fresh 7591´s? Fair i´d say. Nothing i´d write home about but...fair.

Summary is in other words that this unit needs to be torn to pieces and as i do...i might as well run the entire 9 yards. For better for worse.

[NoiseNoiseNoise]

[Racing]

Look. This is why i decided to rip the entire thing apart and i believe it´s quite evident to anyone why....



*gasp*. Yeah well...



Out rear at the voltage selector it had come to the point where rust had formed. So. I attacked the chassis with a wire brush in the rotary grinder and made short notice of it all.
Doing so i of course "hurt" the anodizing too so..



...i opted to spray the chassis silver. Brings that i have to clean all chassis contact points out but hey...looks a ton better. At least IMO.



German. Period. I came to replace the entire wiring for the secondary side of the PT. Had been damaged to the point of no-go by the fire at one point i presume



New is new after all right so... Fresh IEC jack,fresh panelmounted fuseholders and what not. The stock voltage selector i cleaned out before install. New hardware too,of course.



Yes. New sockets as well. Missing one that i´ll pick up later today.



A more elaborate bias board was fabbed. Reason for completely individual adjust is simple,7591´s are rarely delivered as a matched quad,and this then takes out any and all guesswork.
Yep. Replaced the stock main rectifier bridge too.



Of course this needs to be cleaned up a bit but you get the general idea at least. Anything AC is gathered at the chassis one end and done deal.
Fuseholders for both heater circuits have been added and this will hopefully hinder any future fires of the same width as what obviously HAS happend.
For pure looks reasons them fuseholders reside underneath the bias board.



Yes. Even the wiring for the mains breaker got replaced and the breaker itself got handed some well deserved service too.

[Racing]

Seriously. I absolutely LOATHE laying heater wiring down. It is by FAR the most tedious task of a build to me. None the less it needs to be done,it´s that simple.
Still needs to be straightened out (OCD and all that) and handed a few dabs of glue to be kept in place.



Yep. Them the fuseholders for the two heater windings alright. The one for the preamp/PI of course sports a humdinger.

[noisepunk]

Love the look of this one- too bad they decided tremolo was more useful than reverb.

[fat finger]

Is the twisting the part you don't like?

You could try using a pair of safety wire pliers (twisters).

[Racing]

For whatever reason tremolo was all the rage on Euro amps back in the day.
Dunno why that is.

Safety wire pliers,already do.
Nah. What gets me is the itty-bitty part of it. Just boring beyond belief.

[Racing]

Uhu. Feels rather sano to be honest. I like that. That there is the goods for the entire preamp and PI anyhow...



Cooler than snot! DAAAYYYUM! Picked the thing apart and handed it some 400grit emery+ water+ detergent and...well,i guess some would reason that it´s still a bit scarred. Then again....1963..
Jacks i replaced with Cliff ones to make the entire thing floating. I want to be the one that decides where the entire thing grounds...thank you very much..
"Presence" switch (which is a bright switch in reality) will get new tasks in life. Channel switching....



Cleaned the thing out more in depth and reset that piece of plastic. Stock there´s ONE lone 6,3V bulb lighting that there up and...that´s simply not enough so i´ll add yet another one. I want that "Hulk green" to really be dominant all said and done.



New is new after all. This amp uses long shaft pots stock right...and i guess those could be ordered,but who´s got patience to await delivery of that? Nah. I just cut pieces of armored hose to fit and pressed these over the axle ends of the pots. Will thus cut the shafts down on the stockers...and install. To secure the entire thing with glue in turn.

[Racing]

All said and done i went a different route for elongating the pot shafts. Regular aluminium and setscrews did the trick.
In short it sometimes pays off to keep a lathe of your own.



Turned the powertube sockets around. The smaller turretboard is to keep them coupling caps vs the powertubes and the center of said board to keep components for the ECC-82 run effects loop.

[Racing]

Getting there. Have fired the thing up and all stages fire as intended. Voltages about on par where i want them to be,final say will be as i try the amp out.



Jacks and pots for the loop. A little worried about the direct proximity to the speaker jacks but..trials will tell i guess.



Space is getting scarse. Needed a jack for the footswitch control,for channel switch,and due to that rather large piece of sheet metal i fabbed to make the 7591´s fit...this is what it came down to.
Option would be the faceplate and...HELL NO!



AC side of the chassis is starting to get cramped. No harm no foul though as nothing more as far as that needs to be fitted.



PPIMV control had its wiring installed. Seing the proximity vs high tension bits n pieces i opted to use shielded wire. The small solderprongs bolted to the side of each pot is for shield...



Lower breaker is the mains one,which i presume is the stock unit. The stand-by one tho had this really ugly misplaced half crome thingy...so i dug through my stash and came up with a similar one to the mains breaker. Details? Might be...but still...



Law n order gentlemen....law n order...



So. I installed an extra bulb to light that green right...to make the "Hummel" cutout light up like a x-mas tree. Well. Not so much i guess why i´m starting to wonder if LED`s wouldn´t be a better option.?
U guys tell me.

[NoiseNoiseNoise]

LED's all the way for the display.

[Racing]

Uhu.
Might be that you got a point there.

Got to install the "control system". Ie;the switched 5V transformer and the H11 optos. Have wired the thing up to the point that what´s left is to set the tonecontrol up basically.
In short not all that much left to do.