Traynor YCS90 tube selection

[mtlbasslad]

Hello all,
A friend has this Traynor YCS90, seems unable to use Google, & wants me to find him some 6L6-C (HP) tubes. I found them from Groove Tubes (yes I know where they are made & who owns GT now).
However when I check the Traynor service manual, the block diagram says 4x5881 while the schematic says 4xEL34. Seems to me a doubtful swap as the 5881 (or any 6L6 type) is NC to pin 1 whereas EL34 uses pin1
Technical dept. at Traynor says it's OK if I can adjust the bias below -70mv. Customer relations says it's OK because the 2 tube types are so similar... uh, I don't think so.
Am I missing something here?

Thanks in advance for any enlightenment.

[g1]

The pin1 on the board must be wired so either will work. I think if you follow what they said about the bias you should be good (they are talking about 70mV per pair).
Check the value of the cathode sense resistors as they vary in some versions, try to find the exact schematic version for your unit if you can.
Similar to the JCM900's, they go back and forth between the EL34 and '5881' (which should not be confused with NOS 5881). The 5881 they mean are the Sovtek type, or any other proper 6L6GC should do.
Like the JCM900's, they use the same OT's for either EL34 or 6L6.

[mtlbasslad]

Thanks G1, you know I'm out of my depth about checking 'cathode sense resistors' but I can be educated. From tube data sheets I see EL34 pin1 is connected to 'suppressor grid' 6L6 NC. Anyway I'll figure it out...

[Chuck H]

Thanks G1, you know I'm out of my depth about checking 'cathode sense resistors' but I can be educated. From tube data sheets I see EL34 pin1 is connected to 'suppressor grid' 6L6 NC. Anyway I'll figure it out...

Pin 1 on the el34 (suppressor grid) is typically connecte to the cathode at the socket in el34 guitar amp designs. Pin 1 is not internally connected for 6l6 type tubes. So all you have to do to plug in either tube is connect pin 1 on the socket to pin 8. This does mean you can't use pin 1 as a terminal post for the grid stop resistor as Fender did on most of their amps. but this is not hard to reconfigure. With the socket wired this way you can plug in either tube type as long as bias is adjusted and the OT primary impedance is suitable for either tube type. Easy peezy.

The "cathode sense" resistors are just the low value resistors connected from cathode to ground on the power tube sockets. Their value is low enough that it doesn't significantly alter bias. The "test point" for amplifier bias would be from the ungrounded end of that resistor. The voltage dropped across that resistor is analogous to current through the tube/s so bias conditions can be "sensed" as it were. But you need to sure the value of that resistor is accurate for that to work or your bias detections could be wrong. That is what g1 was indicating.

[g1]

Pins 1 and 8 are already joined on the circuit board, so that the amp can accept either tube. I've marked pins 1 and 8 on the picture so you can see the trace connecting them.
The resistors I've circled are the 'current sense' resistors. On this amp they are 2 ohm. That means if you measure 70mV at the test point, the tube current is 35mA. (0.07V divided by 2 ohms).
So, I was mistaken earlier, when I said the 70mV is for a pair of tubes. It's per tube, but means 35mA current because they use a 2R sense resistor, rather than the typical 1R.

I think the YCS90 was consistent using the 2R sense resistors across various revisions. It was a different YCS I was thinking of that you had to be careful about the versions.

[mtlbasslad]

Well guys, you are both doing a great job of leading me by the hand - which for my skill level is quite appropriate. Thanks much. Anyone have any experience with these Groove Tubes 6L6 - C (HP)? A bit pricey...

[mtlbasslad]

Update - cleaned all the tube sockets & all the jacks - finally it was the speaker connection (1/4 inch) that was the dirty scoundrel. Although this amp apparently shipped with 5881 power tubes (which I guess would account for the 90 watt rating?) it's now running JJ 6L6"s, does that make it a 120 watt amp?

[Helmholtz]

Although this amp apparently shipped with 5881 power tubes (which I guess would account for the 90 watt rating?) it's now running JJ 6L6"s, does that make it a 120 watt amp?

No, apart from individual tube variations, output power with 5881s and 6L6s should be the same.

[Chuck H]

Well I don't remember you mentioning there was a problem with the amp in any of this thread. But good on you for solving for it. Those scoundrelous jacks

Please carefully read g1's postings on biasing and those sense resistors. Bias the amp up and let us know how it sounds.

As to wattage... If you have a scope and a signal generator you can measure the wattage for yourself. If you don't, but you have a meter that measures true RMS and any way to put a 400Hz to 1000Hz sine wave into the amp you can get a pretty close measure. That said...

Traynor has proven amazing in regard to what they can get from an amp. Still, don't expect any advertised power to be actual. There was a lot of fudging in print for the "instrument amplifier" game WRT wattage.

[g1]

This is another example of the '5881' meaning the Sovtek version, not the NOS US version of true 5881. Like in the Marshall JCM900 etc.
Yorkville (Traynor) has never designed an amp that used a true 5881, nor have they ever sold them.

[mtlbasslad]

I should explain some things - Chuck H you are right, no mention of any problem in original post. That's because owner was not very forthcoming about what he wanted and I didn't have the amp in my grubby little mitts yet. All he talked about was nobody could find the tubes "he needed" When I finally got the amp I noticed the evil 'frying bacon' sound. I cleaned every contact in sight & tested all the tubes (I have an old Knight tester, I know not the best but...)
All tubes tested OK, finally it was the speaker connector (last one I checked of course). After that the amp sounded terrific, no red plating, so I left bias alone. Traynor suggests 'easy access' to test points & bias & 'no need to remove from cabinet' - but both are tucked behind very hot 6L6's...
I do have a signal generator & a scope if I really needed to know output - I know this - it's LOUD!

I got my info on tube wattages from The Tube Store's website, says there are 23, 25 & 30 watt tubes in the 6L6/5881 range...

In the end owner is pleased as punch & wondering why the L&M 'tech' couldn't find his problem... & thanks to all here I increased my knowledge incrementally,

Thanks guys,
Lorne