SpiderWars
Well-known member
Without getting into the history of why, I have a homebrew build that was built into a Hiwatt chassis/cab. Merren 100W PT that puts 500vdc on the plates at idle. But the OT is a custom Merren 2xKT88 100W U/L. It was originally going to be a mini-Major. Never sounded right so I've changed the preamp several times. Never sounds right and never has the punch or balls of a good NMV Marshall/Hiwatt/et al. It's been moth-balled long enough.
I decided I'm going to just try to make it into an early 70's DR103 but with 2xKT88 at first. Not U/L either. So my initial questions are about the resistor values right around the power tubes like screen grids and bias splitters, etc.
The 4xEL34 DR103 uses 100R screen grid resistors but there is also a shared 470R/10W resistor between the screen supply and the screen grid resistors. This will only be two tubes but I was going to use 270R screen grid resistors and a 470R/10W shared. But I'm wondering if I should increase the 470R/10W since there is only two tubes pulling current thru it (even tho each KT88 has more than each EL34 if were 4xEL34).
The pt grids have 22k grid stoppers and 100k bias splitters so I think it's already fine there. Maybe reduce the 22k stoppers to 5k6?
If it won't give it up after this I'm not opposed to pulling the OT and buying a 4xEL34 Hiwatt (Partridge) style OT.
Here it is in current Wiz-Jube Mod state. I almost hate to tear out that pre...it was a bit of a job. The fish is a sticker I got from a truck stop.
I decided I'm going to just try to make it into an early 70's DR103 but with 2xKT88 at first. Not U/L either. So my initial questions are about the resistor values right around the power tubes like screen grids and bias splitters, etc.
The 4xEL34 DR103 uses 100R screen grid resistors but there is also a shared 470R/10W resistor between the screen supply and the screen grid resistors. This will only be two tubes but I was going to use 270R screen grid resistors and a 470R/10W shared. But I'm wondering if I should increase the 470R/10W since there is only two tubes pulling current thru it (even tho each KT88 has more than each EL34 if were 4xEL34).
The pt grids have 22k grid stoppers and 100k bias splitters so I think it's already fine there. Maybe reduce the 22k stoppers to 5k6?
If it won't give it up after this I'm not opposed to pulling the OT and buying a 4xEL34 Hiwatt (Partridge) style OT.
Here it is in current Wiz-Jube Mod state. I almost hate to tear out that pre...it was a bit of a job. The fish is a sticker I got from a truck stop.
