Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jazrok on October 30, 2025, 09:20:45 am

Title: Sluckey's AB763 Deluxe Lite build issue
Post by: Jazrok on October 30, 2025, 09:20:45 am

Hi,

I've just finished building Sluckey's AB763 Deluxe Lite using 300-0-300 PT and 40w OT, running 2 x 6L6GC.

Everything seems to be working correctly and the amp sounds good but it's not very loud - about the same volume as a Princeton maybe... I was hoping for Vibrolux territory. Also, when I turn the amp up loud there is a throbbing sound like there's a tremolo on.

Voltages seem about right 407v B+1, 215v on PI plates and 250v on V1 plates (which does seem a bit high).

I've tried disconnecting the NFB in case it was phase cancelling but it made no difference.

Any thoughts?

Thanks

JM

I've disconnected NFB

Title: Re: Sluckey's AB763 Deluxe Lite build issue
Post by: shooter on October 30, 2025, 09:28:36 am

where did the bias voltage land?


how many speakers have you rolled through?


don't have Steve's schematic handy, goes the amp have trem??

Title: Re: Sluckey's AB763 Deluxe Lite build issue
Post by: Jazrok on October 30, 2025, 09:42:47 am

I biased it @ 40mv per tube. Playing through a eminence EM12 which is a very efficient speaker.

Title: Re: Sluckey's AB763 Deluxe Lite build issue
Post by: stratomaster on October 30, 2025, 10:41:47 am

Can you measure output power into a dummy load? That's the definitive test for determining if it's outputting as intended.

Title: Re: Sluckey's AB763 Deluxe Lite build issue
Post by: mresistor on October 30, 2025, 10:55:16 am

Quote from: shooter on October 30, 2025, 09:28:36 am

don't have Steve's schematic handy, goes the amp have trem??

no trem  https://sluckeyamps.com/misc/AB763_Deluxe_Lite.pdf

Title: Re: Sluckey's AB763 Deluxe Lite build issue
Post by: Jazrok on October 30, 2025, 07:00:20 pm

can anyone verify what voltages I should be seeing on pin 2/7 of the PI? I have 57v.
Also,
Pin 3/8 = 90v
Pin 1/6 = 215v

Do these sound right?

Title: Re: Sluckey's AB763 Deluxe Lite build issue
Post by: SEL49 on October 30, 2025, 08:09:28 pm

Sounds OK.

Title: Re: Sluckey's AB763 Deluxe Lite build issue
Post by: Jazrok on October 30, 2025, 08:47:07 pm

Quote from: stratomaster on October 30, 2025, 10:41:47 am

Can you measure output power into a dummy load? That's the definitive test for determining if it's outputting as intended.

I don't have that equipment, unfortunately