Traynor YBA-3A 6KG6 to EL509S

[shiner555]

Hi All,

Got a question for you! An amp was brought to me with some tubes that I was not familiar with on the output, 6KG6. After doing much research, found out that they are no longer in production and that it would be hard to find a matched set. I was encouraged to move over to the JJ-EL509s's, which are supposed to be the exact same tube, minus the top cap. This was also after speaking with traynor as they said the output xfmr is custom matched to the GKG6, so trying to move to KT88's may not be a good idea.

So I'm about ready to convert out the 9-pin sockets to the 8-pins for the new JJ's but I noticed that Grid 3 is now tied to the cathode on pin 8 of the JJ's, where it was not tied to cathode on the 6KG6.

In looking at the schematic for this amp, I'm wondering if this is ok!?? I've been told its a direct swap, but this has me scratching my head. Any ideas?

Many thanks!!

Traynor Schematic
http://www.prowessamplifiers.com/sch...al_Yba_3a.html
JJ EL590S
JJ EL509-S
6KG6
TDSL Tube data [6KG6]

[Gtr_tech]

The Svetlana (SED) EL509 has the plate cap....
SED: EL509

[Jazz P Bass]

I believe the Svetlana was a beam tetrode.
Back to the OP's question.
I think you need to reread the datasheets.
The "new" JJ EL509 is wired the same as a EL34 (or 6L6 for that matter)
The old 6KG6 & the old EL509 were interchangeable.
And wired different than the JJ.

[shiner555]

Many thanks for the replies!

I've contacted three SED reps in the US and they can no longer get that tube.....thus the reason to switch over.

JP,

I've looked at the EL34 data sheets vs the new JJ509S and I clearly see that G3 is tied to cathode on the JJ509S where on an EL34 G3 is not. Am I missing something?

Still, what do you think? The data sheet voltages and currents line up for the new JJ509S vs a 6KG6. I just don't know if I can live with G3 tied to cathode in the YBA-3A circuit. Any ideas?

Many Thanks!!

[Jazz P Bass]

Grid #3, gets tied to the cathode (ground)
Kind of like a 6L6 where it is internally connected.
Even on a EL34, where grid #3 is labeled Pin #1, it gets tied (externally) to the cathode (ground)
You will be fine.

[g1]

You will need to disconnect g3 (pin2) from the bias supply. I should think you will be able to compensate for any change with the bias adjustment.

[shiner555]

Guys,

Thanks again for the feedback. Looks like I should be ok!!

G-one,

Excellent note. That was I was concerned with, but I didn't state it clearly in my earlier posts. Question. Any idea on the proper bias for the EL509S?

I see the notes in the traynor schematic to set the negative voltage for -45V, but I wonder with grid 3 disconnected if this is still valid?

Cheers!

[shiner555]

Hey Guys,

Back again! I've finished, or so I thought, the re-build of the traynor. I've re-capped almost the entire amp, sans some of the pre-amp. I've also put in the new EL590S. When I first turned it on, I was getting bad high pitched oscillation on output, then realized that I had flipped the output of the tubes, had them going to the wrong side of the input to the output xfmr. After putting back, things sound real nice at low volumes, but if I try to get some volume out of the amp I get a really bad popping/distortion. Hard to describe so I made a quick video.

http://www.youtube.com/watch?v=zzNsGx41r3A

In looking at the PS output voltages everything seems ok per the schematic. I've gone over my wiring a few times, and I don't see anything.

Anyone have any ideas?

Many thanks!!

[Steve Conner]

I see this is one of the amps that only has screen stopper resistors on two of the four tubes. We were discussing that the other day, how it worked with old tubes but modern ones will oscillate.

And, I think I can see your screen grids glowing when the noise appears, which also suggests some high-powered RF oscillations.

So, try adding two more 47 ohm resistors to the tubes that don't have them. Right at the socket pins as usual for stopper resistors.

[shiner555]

Hi Steve,

Many thanks for the reply. Great suggestion. When I was looking at that earlier today I was thinking e same thing...should have tried it if only I had gotten 42ohm instead of 42kOhm resistors!

One more question. What do you think about the diodes between the center tap of the output xfmr and the other halfs? Should I get rid of them?

[shiner555]

Adding the extra grid stoppers fixed the problem!!! Many thanks again for the suggestion. I really learned a few things on this one. Score one to ampage.org once again!

[g1]

What do you think about the diodes between the center tap of the output xfmr and the other halfs? Should I get rid of them?

The parts shown on the schematic (thyrectors) are for protection. More commonly we see about 3000 volts worth of diodes on each side, often referred to as flyback diodes or spike protection diodes.
Seeing as you mentioned ampage.org, something from the archive: Spike protection? Diodes? - AMPAGE Archive
I have seen some of those actual thyrectors fail in the Traynor's but considering the age of the amps, you can hardly call that unreliable. If they are still the stock parts you can leave them in, or replace with diodes, or some people just remove them and go protectionless.

[shiner555]

Hi Guys,

Digging up this thread. The amp just came back across my bench. Two of the new EL509S were blown after about 5hrs of heavy usage. The two that blew were both on the same leg of the output xfrm. Everything internally looks ok, however I need new tubes to full check it. Any ideas on what to check? Maybe I had it over-baised......just hope it is not the output xfmr!!

[g1]

Make sure you have no DC leaking through coupling caps C22 or C23, whichever is connected to the tubes that blew.

[shiner555]

Hi G-one!

I had to travel unexpectedly for business, my amp work is more of a hobby, and now I'm back on the traynor. I checked it out last night, and everything seems in order. All voltages are correct according to the schematic, bias is stable according to the schematic, and I don't see any more DC, sans the bias DC, after C22 and C23. I put the two new EL509S's in and everything seems ok. Any other ideas on things to check out? I'm still waiting to hear from JJ as to what when wrong with the tubes....just seems weird as basically everything was replaced in this amp sans the XFMRS.

Cheers!!