18Watt.com

From the input Jack to pin2 of V1 is only 2 inches,so do I make a very short shielded cable or risk jumping the grid resistor across?
I found some Marshall plexi reference voltages to compare with the trinity,quite a bit of difference in plate voltages due to the cathode biasing I.e. the trinity has 820R/.68uf and the Marshall 2K7/.68uf I imagine there will be quite a difference in tone as well,will experiment with that one.already replaced the clean boost values with 820R on the V2 cathode.

geoff 1965 wrote: ↑

Wed 05/26/21 6:15 pm

or risk jumping the grid resistor across?

How is that a risk? Do you not trust your soldering skills?

risk as in the resistor leads acting like mini antenna's Josh,or am i being overly concerned there?

geoff 1965 wrote: ↑

Wed 05/26/21 8:13 pm

risk as in the resistor leads acting like mini antenna's Josh,or am i being overly concerned there?

Overly concerned. If they act as antennas, then consider doing something else. But 2 inches isn't likely long enough to hurt anything.

Okay i’ll try that,can do the same with the gain pot as well.

All wiring done now except the couplers to the pots,just waiting for those,initial power up tonight then I can take some voltage measurements and adjust the B+ rail to suit.

Nice work! Are those 1/4" jacks on the rear panel carrying preamp signals? Grounding them to the chassis might be a concern.

Jack

Yes Jack it’s the FX loop and now you point that out the Hiwatt schematic shows no grounding of the loop,can easily cut the grounds if there is a problem.i want that signal wire from the treble pot shielded as it passes over the tag board,I could ground the wire at the pot side if needed.

initial startup good,no smoke or fireworks and zero on the bulb!
I was’nt exactly sure what plate voltages on the pentodes to expect but was looking between 275-300 to be happy.anyway look at the pics i’ve got 303 diode and 285 ez81 rectified with vvr on max. Have to adjust the B+ rail now for the phase inverter and preamp and a thorough test of that vvr mosfet!

Good job, looks great!

Jack

Agreed, it looks awesome. I want to hear it when you're done!

Me too

Thanks for the comments lads,just made the base plate and the B+ rail voltages are done,waiting for the couplers then I can test with a speaker!

Wiring finally done! ungrounded the FX loop and i’ve used a A250K pot for the volume to start with the extra triode to buffer the effects.i used Teflon sleeving for the couplers & resistors.
The only 4 ohm speaker I have is this black star 12” 50W,not ideal but should be okay for testing.will post progress and full voltages.

Just had a moment! I was taking voltage measurements and when I got to the second pentode plate the reading went off the scale so I immediately unplugged and checked the wiring for whiskers etc then I swapped the tubes around and the same thing happened.it was the volume pot on max and it was overloading the phase inverter,backed it off and everything was good so I have some attenuating to do there which I expected.going to rig the speaker up so I can hear when attenuating the signal and swap the 250K pot for a 100K.

Vvr problem!! just done a test of the voltage sweep on the vvr unit and this is what I got,minimum 31V,one third turn 1200V!!,two thirds turn 600V,maximum 312V. luckily all the tests i’ve done so far we’re on full 312V. this is the vvr,the 100K goes to the pot wiper and the diode to the input lug with a 100K to ground from lug 3.

Well, it can't really be +1200V, can it? May be it's oscillating and fooling your meter.

Jack

Was it under load or isolated from the circuit when you tested?
Dd

it was in circuit under load Dd,going to remove the valves and retest on both diode & ez81 rectifier and use both of my multimeters to see if it's an oscillation like Jack mentioned.very quickly as i don't want to damage anything i.e. OT or filter caps etc.

I think you need a scope for this. Or try it with your meter on an upper range of AC volts.

Jack