So my last post was about this lovely Traynor YGM-3 and specifically what to do about that high EL84 eating plate voltage.
The solution I tried was to use the Sovtek EL84M, rated for higher current and a whopping 500V on the plate. The amp left here sounding lovely.....
But, well, that didn't work. In this business one is always experimenting, largely to keep the cost reasonable. This is an expensive business. And I don't like seeing a customer return for a long time. It's not ideal for them especially.
And I'll just say it. I'm not here to sell anything, not even my services. So I can be honest here.
New tubes suck. It's just a fact we need to live with. The world will never produce another RCA, Mullard, Tung Sol, Western Electric, General Electric, Mazda, National Union, Amperex, Brimar or genuine Telefunken tube again. There is absolutely no incentive to do so. We need to live with the mediocre in this world now. Music is changing, the world is changing. There will be no exceptional tubes ever made again much like there may never be another platinum record again. It's over. Music is free, the population of guitar players and audiophiles is diminishing. I love tube amps. I find them fascinating so I carry on. And I will play music till the day I die and I will sound my best till then so that is that.
So what happened? My client got home and rocked it out for a couple rehearsals. It sounded great then it ceased to sound great. One tube totally died, the other test about 1/2 on my TV7 tester.
Not acceptable.
There are several ways to drop voltage. Zener diode, dropping resistor. But I don't like those methods. Since my client wants this to be road ready we opted for the most expensive route: changing the power transformer.
I used a nice Canadian made Hammond, part number 270DAX. I write this so I can have a record of it. If I see another amp I can just tell them their options if they want reliability.
With the original transformer the B+ sat around 425-440vdc. With this part depending on bias its between 329-345vdc. About the same range as your Blues Jr. Those run hot but they are reliable. I think this is a safe range.
You do lose a few watts. But the amp sounds as good as it did before, a tad warmer my ears say.
Nice thing about this part is it's the same size as the original. You need to get creative with some washers to run the heater wires around to the chassis hole, drilling is not an option here, and with that I had no need to drill anything. It's a 520 vCt transformer so you'll need to take out the 2 diodes going to ground and put the red/yellow CT wire to where the diodes terminated otherwise you'll have some seriously high voltage problems!
Once that's done you'll need to change the bias resistors until you get an acceptable range. In this case I changed the 18k coming off the AC feed to a 10k and replaced the 22k with a 7.5k tied in series to my 20k trim pot. Now the amp is sitting at 329vdv with 22ma on the output tubes. That's about where a Blues Jr sits.
So in conclusion, if you have one of these this is a good path to reliability unless you have the dough for genuine 7189 tubes. It's worth doing. I still maintain this is a great amp. Now it's a great amp for modern times.
JB
The solution I tried was to use the Sovtek EL84M, rated for higher current and a whopping 500V on the plate. The amp left here sounding lovely.....
But, well, that didn't work. In this business one is always experimenting, largely to keep the cost reasonable. This is an expensive business. And I don't like seeing a customer return for a long time. It's not ideal for them especially.
And I'll just say it. I'm not here to sell anything, not even my services. So I can be honest here.
New tubes suck. It's just a fact we need to live with. The world will never produce another RCA, Mullard, Tung Sol, Western Electric, General Electric, Mazda, National Union, Amperex, Brimar or genuine Telefunken tube again. There is absolutely no incentive to do so. We need to live with the mediocre in this world now. Music is changing, the world is changing. There will be no exceptional tubes ever made again much like there may never be another platinum record again. It's over. Music is free, the population of guitar players and audiophiles is diminishing. I love tube amps. I find them fascinating so I carry on. And I will play music till the day I die and I will sound my best till then so that is that.
So what happened? My client got home and rocked it out for a couple rehearsals. It sounded great then it ceased to sound great. One tube totally died, the other test about 1/2 on my TV7 tester.
Not acceptable.
There are several ways to drop voltage. Zener diode, dropping resistor. But I don't like those methods. Since my client wants this to be road ready we opted for the most expensive route: changing the power transformer.
I used a nice Canadian made Hammond, part number 270DAX. I write this so I can have a record of it. If I see another amp I can just tell them their options if they want reliability.
With the original transformer the B+ sat around 425-440vdc. With this part depending on bias its between 329-345vdc. About the same range as your Blues Jr. Those run hot but they are reliable. I think this is a safe range.
You do lose a few watts. But the amp sounds as good as it did before, a tad warmer my ears say.
Nice thing about this part is it's the same size as the original. You need to get creative with some washers to run the heater wires around to the chassis hole, drilling is not an option here, and with that I had no need to drill anything. It's a 520 vCt transformer so you'll need to take out the 2 diodes going to ground and put the red/yellow CT wire to where the diodes terminated otherwise you'll have some seriously high voltage problems!
Once that's done you'll need to change the bias resistors until you get an acceptable range. In this case I changed the 18k coming off the AC feed to a 10k and replaced the 22k with a 7.5k tied in series to my 20k trim pot. Now the amp is sitting at 329vdv with 22ma on the output tubes. That's about where a Blues Jr sits.
So in conclusion, if you have one of these this is a good path to reliability unless you have the dough for genuine 7189 tubes. It's worth doing. I still maintain this is a great amp. Now it's a great amp for modern times.
JB
Great post, I am in the UK and have the same amp. I am going to try the 370dax with the multi tap primary, as we are on 240vac.
ReplyDeletewent with the 370EX instead to fit the same as the A1314E tranny.550 CT instead of the original 620. Has to be the 'X11' size from Hammond I think also.
DeleteGreat! I'm happy to know this post was useful. Thanks for sharing!
DeleteI just picked up a 1970 YGM3 that needs a new power transformer. I like your idea of using the 270DAX, but could you explain the center tap and diode change you mentioned. I am relatively new to tube amp repair and could use some help.
ReplyDeleteThank you.
Hi.
ReplyDeleteVery good question. As I'm looking over schematics I'm realizing there were two versions (at least) of this amp. One with a center tapped power transformer and one without.
If yours has the red / yellow center tap wire the install should be easy.
Now if your amp is the other version, with no center tap, I can't say I recommend messing with it. I would take it to a good technician.
I did this job many years ago and don't remember the particulars but looking at schematics for both, the non CT one is a job to be tackled by someone with experience. I don't remember exactly what I did but typically you would simply disconnect the two diodes going to ground which create a ground reference, then simply connect that CT wire to the standby switch. But it doesn't appear to be as simple as that.
Hopefully yours is the CT version!!
If yours happens to be the one with a center tapped power transformer you should be able to to just drop the Hammond in there and the center tap gets wired to the standby switch.
Copy and paste:
https://elektrotanya.com/traynor_ygm-3_ygm-4_sch.pdf/download.html
That's the non CT power transformer model.
And here is the model with a center tapped transformer:
https://www.thetubestore.com/lib/thetubestore/schematics/Traynor/Traynor-Guitarmate-YGM3-Schematic.pdf
Pretty sure when I did this job I just copied the CT version then made some tweaks for the bias.
But like I said, and I can't stress this enough. This is a job for someone with experience. No room for error.
Thanks! J