Fresh 5e9-a build sounds great but has two minor issues

[mort]

1st is the depth/intensity control on the vibrato. Vibe works great but when the intensity pot is past 8 the volume drops out. No idea how to troubleshoot this.

2nd is the plate voltage is abnormally low to both sides of v1. There's 241.6 B+ supply at the junction of the two 100k resistors and 81v on the plates. Cathodes have 2.9v. The PT is a lower B+ version so the B+ nodes are 359.2 > 332.1 > 241.6. Seems like that 80v should be at least 100v or better. Not sure if I should leave well enough alone or maybe lower some of those supply resistors values to let the voltage up some.

http://www.thevintagesound.com/ffg/s...9-a_layout.gif

The thing sounds great though. The guy shelled out for the Celestion Blue speaker and Mercury xformers. I hadn't used Mercury before and I can see why people like them. They seem to hold a strong signal, sound edgier and with more presence. Some may not prefer that difference. I don't see it as better or worse, just different.

[Tom Phillips]

...The guy shelled out for the Celestion Blue speaker and Mercury xformers. I hadn't used Mercury before and I can see why people like them. They seem to hold a strong signal, sound edgier and with more presence. Some may not prefer that difference. I don't see it as better or worse, just different...

Cool, but unless you did a test changing only the transformers, how do you know the Mercury transformers are responsible for the "strong signal, sound edgier...with more presence?"

[mort]

Cool, but unless you did a test changing only the transformers, how do you know the Mercury transformers are responsible for the "strong signal, sound edgier...with more presence?"

While it's not uber scientific, I've built a bunch of different circuits out of the same brand transformers, tubes, caps etc over teh last year and have gotten used to what to expect out of that combo of parts. Introducing a different set of transformers was pretty easy to hear.

Do you have any comments that would address my questions?

[Chuck H]

I think you're right that the voltages on V1 are too low. But your cathode voltage is over spec for the stock, higher voltages. Check the value of the cathode resistor for that tube. If it checks out you may want to try another tube in location just to eliminate that as well.

[Tom Phillips]

1st is the depth/intensity control on the vibrato. Vibe works great but when the intensity pot is past 8 the volume drops out. No idea how to troubleshoot this...

It is likely that the high intensity tremolo is putting the power tubes into cutoff. Address the bias issue that you are discussing with Chuck H first. It may solve the tremolo problem too. If no then we will go on from there.

[mort]

cathode resistor and cap measure as normal. I don;t have another JJ 12ay7 (ecc82) so I subbed in a 12ax7(ecc83) and now the voltages are 280.7v on the B+ node, 1.6v on the cathodes and 186.5v on the plates.

The Fender drawing shows 290>150>2.4 and now I've got 280>186>1.6. Doesn't that seem a little odd?

Also, can I now assume that the ecc82 is bad and return it?


edit: oh yeah and the depth control got better but still wants to take the volume down at the very tail end of the sweep. When the depth is maxed there's only guitar sound coming through at one end of the pulse.

[frus]

cathode resistor and cap measure as normal. I don;t have another JJ 12ay7 (ecc82)

ECC82 = 12AU7, not 12AY7

it's a very different tube, and I'm not at all surprised that it biases strangely

[Justin Thomas]

D'oh! Good catch! Yeah, I reckon there's a difference between a gain of 44 v. ~18!
I've made that same mistake before; thinking 6201 & 6072 were the opposite of what they were. One's 12AT7, one's 12AY7.

I don't think there IS a direct ECC__ replacement for a 12AY7?

Justin

[mort]

Well I'll be dipped in pickled pears, I don't know what made me think it was a 12ay7. It says 12au7 right on my order. I must have had a blonde moment

[Jazz P Bass]

Pickled pears?
I would add 'star anise'.(Illicium verum)

[mort]

I was just going for some good ol alliteration

[Chuck H]

I'd say that the behavior of the ax7 in that position indicates the circuit is working correctly. You could try an ay7 if you like, or just leave the ax7 in there if the tone suits you. I might be inclined to do that since IMHO preamp triodes seem to sound best over 120V. I'm basing this on my experience with ax7's though. The ay7 will probably land around 110Vp. I've liked the tone ay7's whenever I've tried them as ax7 subs. It is the tube the circuit was designed with so it's worth plugging one in to see. And, of course, my tastes for tone (plate voltage or otherwise) don't apply to anyone but me.