bogen ch30 hack.

[DummyLoad]

got a bogen ch30 from an old friend. pretty sorry condition. rusted cover, UV damaged purple paint, rust is coming through the silver hammertone of the cover and it's pretty bad in some places. it will need sand-blasting an refinishing.

before starting, i noticed that the OT paper jacket was burned and i suspected the OT was possibly burned - it was; 1/2 primary opened up so i hacked in a NOS hallardson branded OT that's rated @ 35W, 6.6K primary that i had gathering dust.

stock grid leak 6SC7 pre-amps weren't getting it done, nor was the summing amp.  modded the pre-amps and summing amp is just a paralleled gain stage now. originally designed to use 6L6G outputs and 5U4G recto. one of the 6L6G is fried, so i upgraded to 5U4GB recto & 6L6GB output tubes, second stage is coupled to a spin of a james stack minus the bass control. the PI is the stock paraphase with lower value coupling caps than on the original.

cool sounding amp - love the tone with single or blended pre-amps. plenty of low end, and feeds back well. i opted for no NFB on this one as i didn't want to hack NFB into the stock PI, nor did i want to convert it to a LTPI - yeah, i got lazy... :-/  

schematic attached. photos coming shortly.

--DL

[tubenit]

Very nicely done!  I'm impressed.   I think that would be a sweet amp.

With respect, Tubenit

[DummyLoad]

[DummyLoad]

last hack and it finds a new home... i split the inputs - plug into J1 and both CH1 & CH2 are active; plug into J2 and only CH2 is active. found another ST bottle 6L6G that matches the survivor - amp now has all ST shape power bottles - neat looking stuff.

schematic attached.

--Dl

[Platefire]

DL

Kool project. To me it's fun to do a hack job occationally where there is no worry about cosmetics/finishing, just functional electronics. Since you started the post as a finished project, I was wondering how long overall it took?  I never have been able to pull one off as a weekend warrior project--I'm just to slow  Plate

[RicharD]

I test drove this amp last night and kinda feel responsible for causing the last tweak.  The amp has a ton of drive and when running the parallel V1 pushed hot, it had a lot of sizzle which I thought took away from the schweet tone control.  The tone control is very very nice.

[RicharD]

Ah, looking at the input jacks closer, you did what I was talking about.  Kewl!

[DummyLoad]

much thanks all.. 

plate - it was a weekend warrior project. i got the amp friday after work. most the chassis machining was done that evening. the assembly work was done over saturday and i fired it for the first time sunday morning. i put the finishing touches on it last night after richard took her for a test drive.

thanks for the input richard, much appreciated - it was instrumental to the overall success of this little project.

another vintage bogen saved from the scrap heap... :-)

--DL