Traynor YCV40 Low B+

[bobloblaws]

Hey guys, I have a Traynor YCV40 here (partial schematic attached), it has no sound despite everything being lit up, including tubes. The first thing I checked was plate voltages. Sure enough they are way low, in the neighborhood of 60 VDC for the power tubes and 30 VDC for the preamp tubes. I then measured AC supply coming from the transformer, seems normal, aprox 320 VAC. On the other side of the rectifier diodes (e.g. D7, D8) I'm seeing about 435 VDC, also seems normal. However, at point "A" I only see 66 VDC. I get similar readings at points between D12 and C28, between D13 and R102, and between R101 and R103.

So I have a couple of questions.

1. What is the purpose of this section of the circuit that contains Q8 and Q12 and adjacent resistors and diodes?

2. What are the possible causes for the low voltages and which is most likely (if applicable)?

Thanks,
B.

Schematic

[Enzo]

It is a voltage regulator circuit.

D13 is a 10v zener, is ther 10v across it? Is R100 open? Is Q12 shorted? It isn't a complex circuit, just check those parts to see.

[g1]

Make sure you have the exact schematic as there were many revisions. Originally that regulator circuit was also tied in to the HV standby and acted as a solid state switch so they could use a low current standby button.
Later the standby became just a mute for the audio.

[bobloblaws]

Make sure you have the exact schematic as there were many revisions. Originally that regulator circuit was also tied in to the HV standby and acted as a solid state switch so they could use a low current standby button.
Later the standby became just a mute for the audio.

Yes, thanks. To be honest the schematic I have is not exactly the same version, it's close. For the life of me I couldn't find the correct version, I have sent an email to Traynor/Yorkville requesting it. For the record the PCB in question is labeled M581 3.00 and the PCB for the preamp section is labeled M581 4.00 in case anyone knows where I can find the corresponding schematic.

Edit: I just found this thread with same or similar problem. The schematic mojotronix uploaded lines up better with my amp e.g. U3 is present in my amp.

http://music-electronics-forum.com/s...ad.php?t=40454

[bobloblaws]

It is a voltage regulator circuit.

D13 is a 10v zener, is ther 10v across it? Is R100 open? Is Q12 shorted? It isn't a complex circuit, just check those parts to see.

So I replaced U3, Q8, Q12, R100, and D13 because when I was troubleshooting a couple of days ago my probe slipped and I shorted 2 pins on Q8 and blew it up along with some adjacent components, so it's hard to say which one(s) were the original culprit(s).

Enzo, you expect to see about 10V across D13? The amp is back up and running and I'm only seeing 4V across it.

Traynor informed me they do not have the schematic for the my revision. Here is the closest manual I've been able to find. The schematic in this one is dated Sept 3, 2002 which corresponds to PCB version 7.10 in the revision history in newer versions of the manual. My board is version 4.00 from June 21, 2001. I'm uploading the revision history as well.

Manual-Service-YCV40-1v2.pdf

[g1]

If it's all up and running, then I'd expect D13 is just a clamp to prevent an excess of 10V between G & S. (assuming you used 1N5240 )

[bobloblaws]

Yes, here's what I used: https://www.digikey.ca/product-detai...SCT-ND/1532770

G + S?

In any case, I reckon I misunderstood Enzo's comment re: 10V

[J M Fahey]

Not sure about the current situation:
* do you still have that low voltage?
* what does Point A feed? ... you do not show that VERY IMPORTANT point.
* does it feed screens only or OT and power tube plates too?
If so, I am intrigued why would they regulate +V on a tube guitar amps.
"Solving" a non problem and potentially introducing lots of issues.

I mean, IF it were some kind of Power Scaling, it would serve a purpose, but ... as is .... żżż???
I see no voltage adjustment anywhere.

[bobloblaws]

Not sure about the current situation:
* do you still have that low voltage?
* what does Point A feed? ... you do not show that VERY IMPORTANT point.
* does it feed screens only or OT and power tube plates too?
If so, I am intrigued why would they regulate +V on a tube guitar amps.
"Solving" a non problem and potentially introducing lots of issues.

I mean, IF it were some kind of Power Scaling, it would serve a purpose, but ... as is .... żżż???
I see no voltage adjustment anywhere.

All good now, Jaun.

Per the schematic in the manual I subsequently uploaded, A goes to OT center tap and 6L6 plates, B feeds screens.

Here's an earlier revision, # 6.20. schematic_ycv40_M581-6.20.pdf

[bobloblaws]

Not sure about the current situation:
* do you still have that low voltage?
* what does Point A feed? ... you do not show that VERY IMPORTANT point.
* does it feed screens only or OT and power tube plates too?
If so, I am intrigued why would they regulate +V on a tube guitar amps.
"Solving" a non problem and potentially introducing lots of issues.

I mean, IF it were some kind of Power Scaling, it would serve a purpose, but ... as is .... żżż???
I see no voltage adjustment anywhere.

FYI, I asked the YCV tech at Traynor/Yorkville what problem that regulator circuit was intended to solve. Here's his reply:

"Regarding to that circuit, it just add current limit, in-case something goes wrong with the tubes (doesn't work all the time!) & less noise and hum on the high voltage lines."

[g1]

G + S?

In any case, I reckon I misunderstood Enzo's comment re: 10V

Gate and source of Fet Q8 as labelled on schematic.

If so, I am intrigued why would they regulate +V on a tube guitar amps.
"Solving" a non problem and potentially introducing lots of issues.

FYI, I asked the YCV tech at Traynor/Yorkville what problem that regulator circuit was intended to solve. Here's his reply:

"Regarding to that circuit, it just add current limit, in-case something goes wrong with the tubes (doesn't work all the time!) & less noise and hum on the high voltage lines."

When these amps first came out (2000), I enquired about the circuit. They told me that a hardware type high current standby switch cost dollars, where a low current button switch and silicon current switch could be made for pennies. At the time, Traynor had not been making anything with tubes for decades. I tend to believe that reasoning (bean counter) or it may have been an over-zealous designer with a 'cool' new idea.
Anyway, there were a lot of failures. The standby button switch has morphed into an audio mute, and the HV is no longer switched in standby. The 'regulation' aspect of the circuit has been kept for whatever reason. Maybe it saves on HV caps as they are using 10uF's after the reg.?
The standby in new versions just disconnects the cathodes of the power tubes.

[J M Fahey]

I guess they were optimistic.

If power tubes short, the current limit Mosfet will have to dissipate the full +V times the current it was set to, which of course must be higher than any expected current peak under normal use.

That product gives a very high dissipation which I doubt the MosFet can stand, at least more than a couple minutes ... if that much.

If anything, they "should" have set it up as an "automatic Standby OFF" switch, triggered by overcurrent, say like a solid state relay.

MosFets can *switch* lots of Power safely; now if you make them *dissipate* high power, silicon is silicon, thermal resistance is thermal resistance, high dissipation will overheat that 1/4 pinky nail sized wafer and above 200C it´s History.