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[IslandPink]

Ah, sorry if I upset you Wolfgang. I like a lot of different types of music myself. Steve has well explained the thinking behind my comments.

[Greg]

Reaches for his Dusty CD to see if anything suitable.

Give it a wipe over and I’m sure it’ll be fine

[Cressy Snr]

ISWYDT

[Greg]

Now this OTL, in conjunction with the Fane single driver speakers, certainly does classic rock’n roll/soul/r&b better than anything I’ve built in the past, and I’ve decided that this type of music is what I’m going to show the system with and damn the consequences. At least I’ll have been true to myself.

Good for you,Steve. I’m really looking forward to hearing you OTL. I know it may be a space issue, but if you could bring the Fane’s as well, that would be the icing on the cake. I loved your big Metronomes. As you say your system is the best you’ve ever done, I really want to hear the full combo.

[Cressy Snr]

I’m bringing the Fanes too. I reckon they’re the only speakers at that’ll be at Owston with which the OTL has any chance of making anything above a whisper. One was designed with the other, so they come as a unit.
I believe it’s the best system I’ve built; others can feel free to disagree, as is their right of course

[Ali Tait]

Wouldn’t mind playing my OTL’s on the Fanes if that’s okay with you Steve?

[Cressy Snr]

No problem Ali.

[Ali Tait]

Grand. Be interesting how it compares to a single valve OTL.

[Wolfgang]

If this is directed at me I need to ask.....What defense mechanisms?

This wasn't directed at you, Steve. It was fun to follow this thread and how you approached each step.
Obviously it needs more background information for someone who is not part the "inner circle" of this forum in order to be able to follow a certain style of banter properly.

[Cressy Snr]

Well here’s a thing. Because the 6N1P worked so well in the amplifier, I thought to myself, why not try the ECC88/6922, just out of curiosity. I thought I had a few, but sod’s law dictated I would only be able to find one of the buggers.
A quick email to Simon, earlier today, turned up a couple of Chelmer 6922s, so I picked them up from his place earlier this evening. While I was there, Simon offered me a couple of 6CG7 to try out too. These are as most of us will know, the 9 pin equivalent to the ubiquitous 6SN7. A quick check of the pinouts confirmed they were compatible with the PCB mounted socket numbering on my driver boards.

The 6922s unfortunately, were a dead loss, as their high transconductance compared to the 6N1P, even though the gain was the same, made sure that all they did was oscillate and buzz as soon as the HT was applied. They did settle down after a few seconds of sounding like a wasps in coke cans but this was not ideal, so they had to be rejected in the absence of suitable grid stoppers.

The 6CG7s went in next. They, like the 6SN7 will work at 90V on their anodes, so the HT I had was sufficient to make them operate. These sound really rather nice. Not as much gain as the 6N1P, in fact the gain is about equal to the original 6H30pi driver stages. The 6CG7 at low voltage sounds great.

The differences between the 6H30pi, 6N1P and 6CG7 are not make or break, but are more a matter of taste than anything else. Whatever driver stage you use in this amp, it remains a great music maker.

[Cressy Snr]

More news on the 6CG7 as input/driver stage:
Low level treble detail is really rather good, so it does the tinkly bits very well.
Piano tone is spot-on and vocals are excellent across the board, from Sarah Vaughan to John Lennon. In comparison the the Russian valves, the American 6CG7 is a bit more sophisticated sounding. I like them a lot.

I’d say to Ray that it’s worth rolling 6H30pi, 6N1P and 6CG7 to see which version of the music you prefer, as the one you choose will of course, be system dependent.

[Cressy Snr]

Further on again:
Did some measuring of voltages and both the 6H30pi and the 6GG7 produce decent operating points of 2V and 6 or so mA of current, with around 108V on their anodes from a 165V supply. Both look decently linear on the curves for each valve. Both valves sound nice and clean driving the output stage.

The 6N1P only runs at 3mA with 1.5V and 130V on its anode, from a 165V supply. This is down in the basement as far as the curves are concerned, but nevertheless it still sounds very good, probably a lot of even harmonic love going on with this valve, which probably accounts for its “nice” sound in this circuit.

Measurements seem to correlate well with the sounds in this situation. I’m rambling now.

[IslandPink]

It's great when you're at the stage of detail work like this, and getting positive steps. Good work !

[Cressy Snr]

Yes, it’s nice when you get to this stage with a project.
The measurements I took were initially to make sure I was not running the alternatives to the 6H30pi drivers at levels that could have caused them harm. It was later that I began to link the measurements to the sounds I was getting from each tube.

This project is a real cooperative piece when I think about it:

3 off 13E1 from Steve S to go with my remaining good one.
2 off 6CG7 from Simon
HT transformer from Phil
Driver stage PCBs (three versions) from Ray.
Original breadboard 5687s from Nick ( must give them back at Owston)
Plenty of engineering input from Wolfgang.

[Mike H]

These are as most of us will know, the 9 pin equivalent to the ubiquitous 6SN7.

Actually I didn't know that.

Just don't fiddle with it 'til you break it.