18 watt voltages after build

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

Moderators: CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

Post Reply
User avatar
Bieworm
Verbose Moderator
Verbose Moderator
Posts: 2287
Joined: Mon 02/10/20 8:24 am
Location: Belgium

18 watt voltages after build

Post by Bieworm »

OMG!!!
Amp sounds fine, but voltages on V2 and V3
are off spec.
15818787655945983238855974667501.jpg
Looks like the transformer doesn't deliver 2x3.15V ..I measure 2x2.7V
The components in the PI circuit are within specs. I checked. I don't know , but 15% less current on the filaments seems like a probable cause to the low measurement on the grids...or am I wrong?
The platevoltages on V3 are also off... pin 1 = 184V and pin 6 = 130V... Any ideas?
The cathodes measure 1.43V at pin 3 and 8. This is nearly 50% too much.
FWIW the amp sounds amazing nevertheless. Plugged in at 4Ohms into the 3x10 VK cab (2.66Ohms)

Important notice:
1. since I only have a Hi input on the trem channel, I only put a single 22K resistor between the input and pin 7 on V3 (that should be about right, no?..I copied it from the TMB schematic)
2. my intensity pot is 5K instead of the 1K on the layout... the reason is that I do not have a 1K available..
You do not have the required permissions to view the files attached to this post.
0 x
"THIS should be played at high volume..preferably in a residential area"

Post Reply