ODS Inspired Build; #102 Values with Buffered FX Loop

[timrobertson100]

Great looking build Glenn

The OT phase test info would be a good addition for the FAQ section too

[GAStan]

Very interesting build Glenn! Impressive figuring it all out like you did. Way above my cranium, lol.

Thank you Raoul. It's been a challenge for sure, but one I've enjoyed. I've enjoyed watching your builds, please keep posting them.

Great looking build Glenn

Thank you Tim.

I haven't spent any time with this lately but hope to this weekend. I need to post some voltages and get some opinions about them.

[GAStan]

Voltages:
B+ 450; B+2 448
PTs: 33.5/37.8 & 32.3/37.7mA
~17 watts/56%
Sovtek 6L6WXT+

B+3 430
PI 286/29

B+3a 387
FX2 251
B+3b 383
FX1 383/103 (Cathode Follower)

B+4 317
OD1 192
OD2 201

B+5 310
CL1 190
CL2 193

Heaters 7.0vac (a bit high)
Input 123 vac

[GAStan]

I put in some JJ KT66 power tubes I have to see what it would do for the heater voltage. They brought it down to 6.9vac. They sound great in this amp. Good highs. Brite. I see how they could cause the Ice Pick effect but luckily it's not bad in this amp and can be dialed down. The lows are nice and solid. Mids are good. I can see why these would be suitable for HiFi use.

FX loop has 60hz on it. Could just be the tube but first I need to address the CF plate voltage. It's at 383vdc while Martin's values I used have it at 260. I put in the wrong power filter dropping resistor, 2k2 installed should be 100k. The plate voltage on the other tube needs to come down a bit too, it's currently at 251. I'm going to change this before powering it up again.

Dumbleator_Update_MPM.png

[martin manning]

For the built-in D'lator I believe the best plan is making the D'lator signal grounds at the loop jacks. Do you have a branch off the screen filter for the loop power? That should be pretty clean; the negative leads of the extra filters can be grounded with the screen filter.

[GAStan]

Grounding as follows:

B+1 ground to chassis near rectifier/bias board with HV center tap, and rectifier/bias.

B+2 & 2b to chassis near power tubes.

B+ 3, 3a, 3b, 4 and 5 (on filter board these are all tied together) to chassis near input jack with CL, OD, FX and PI grounds. Input and FX jacks isolated and grounded with these too. FET also grounded here.

I'm certain the hum in the FX is the tube. CL had the hum, swapping CL and FX the hum followed the tube. It isn't horrible but definitely there. I'm sure the voltages aren't helping, cathode on CF is about 100vdc.

The FX power comes off B+3, PI filter section. Currently B+3>22k>B+3a>2k2>B+3b. I need to increase the 22k a bit and 2k2 a bunch. I'll got some values from 22k to 33k to try, then 2k2 up *to 100k* for the other one. Sound like a good plan?

*edit*