Tubelab Simple P-P

[zman01]

Thanks Chris.

[kerontt]

I have two options for output tubes. The Harma el84 cryo and the tad str cz. Which is better for Hammond 1650fa opts? I'm using a Hammond 372JX for mains.

[kerontt]

I have a Hammond 1650fa opt and Hammond 372JX. What are some good el84 tubes some of you guys have used on the spp with good results?

[rknize]

If you are looking at modern production, there are really only two types.

JJ makes an EL84 that is pretty tough. My SPP has a bit too much B+, but the JJ tubes laugh it off.

There are the ones made by New Sensor, which are all based on the Russian 6P14P design. They are marketed by New Sensor under a variety of names, brands, and prices. If it is new production and not JJ, it's probably New Sensor. They generally work fine until you push a bit too hard on the B+ front. Their screens can't handle voltages much over 300V. The 372JX should put you close to the edge, but still safe. I can't run these in mine, which uses a 373CZ.

[kerontt]

Thanks for the advice Russian. I will get the cryo jj. I will eventually get the psvane el84. Have you used the cryo valves?

Keron

[rknize]

I have not used anything exotic like that.

[rmyauck]

Adding fixed bias, even with Dave Gillespie's fixed bias EFB Mod would enable you to get the tubes dissipation to the safe level with any production tube. It can be added to any EL-84/7591 PP amp.

Dave's Lab

[kerontt]

Ok guys u finally got the trannies and the chassis sorted out. Ive started the wiring but I'm stuck. How do I wire the primary on the opt. Which is the scr gr and the plate? Another thing is do I have to ground the chassis to the board?

[rknize]

Well, this is the wiring diagram for the Hammond 1650FA OPT:



Each channel on the SPP has 3 sets of terminals for the OPTs. So for example, from left to right along the back of PCB:

Left Channel

• L-PRI_2
  • 2 - V102 screen - primary blue/yellow wire
  • 1 - V102 plate - primary blue wire
• L-PRI_1
  • 3 - V101 screen - primary brown/yellow wire
  • 2 - V101 plate - primary brown wire
  • 1 - primary red wire
• L_FB
  • 2 - Ground - secondary black wire
  • 1 - Feedback - secondary (green, yellow, or white)

Right Channel

• R-PRI_2
  • 2 - V202 screen - primary blue/yellow wire
  • 1 - V202 plate - primary blue wire
• R-PRI_1
  • 3 - V201 screen - primary brown/yellow wire
  • 2 - V201 plate - primary brown wire
  • 1 - primary red wire
• R_FB
  • 2 - Feedback - secondary (green, yellow, or white)
  • 1 - Ground - secondary black wire

Please note that L_FB and R_FB are mirrored! Also note that if you do decide to use feedback (by installing C101/201), you may need to swap the PRI_1 and PRI_2 secondary connections on each channel to get the right phasing (leave the red wire where it is). I can't remember if I had to or not. You'll know if it's wrong if you get loud squealing out of your speakers with feedback connected.

[kerontt]

Have a constant hum in one channael. Swapped the tubes around and it's still in the same channel. Any ideas?