Traynor YBA-1 to 1987 Conversion

[marshallnoise]

So I am now using the dedicated 63vac bias supply line. I had to drop the bias dropping resistor to 10k which put my post bias diode voltage at -53vdc. At the 220k junction I get -44vdc and my range was -33vdc to -43vdc. At 467 plate voltage, I should be right at 37ma.

It took trial and error to get the dropping resistor to the right value. It didn't seem linear or logarithmic so calculating it was tedious.

I'll report how thee voltages look tomorrow with the EL34s in.

Oh, and I just figured out that I shouldn't be running 300v 18 gauge wire all over the place. Apparently the insulation is what keeps the voltage rating low. I ordered new 600v wire from Valvestrom and I will have to rewire all the powerful high VDC stuff.

[marshallnoise]

Allright!!! We have sound! And it sounds really good! I ordered a set of Cliff Jacks in case I need to replace the speaker jacks and the input jacks, but I don't think I will at this point.

I do have grounding issues. When the amp is on and in run mode, I get buzzing that gets louder with the amp volume. At this point, there is no guitar plugged into any input. When I touch the chassis, the buzz goes mostly away. But there is still a buzz. When I plug a guitar in, same situation (obviously).

All of the diagrams of Switchcraft style jacks have no ground wired, presumably because they are grounding to chassis. I think I need to ground them to the control pot buss. Confirm deny?

THESE ARE NOW OLD PICTURES, I WILL POST UP THE NEW PICS WHEN THE AMP IS SORTED

Current input jack wiring.


Control pot buss.


Long view of chassis.


Now, the original Traynor YBA-1 had a 180ohm 15Watt resistor soldered to ground from the Output Transformer center tap on the output jack to ground. See pics below. It is important to know that this amp has a single 8ohm Output Transformer tap. That's all I get.



Here it is as currently wired with no reference to ground.


Before, when I was testing the amp, I remembered the 180ohm resistor and said to myself, well something was going to ground, I should just ground it. Because of this, I was basically getting no output from the amp. Once I cut the ground wire out, full volume was available, but it had that buzz.

I am so very close to getting this thing done, any help would be amazing.

Thanks!

[marshallnoise]

I have decided to just wait for the wiring kit and Cliff Jacks from Valvestorm to work on the amp any more. When I receive those, I will upgrade the higher voltage lines with 600v rated wire and also implement Larry's grounding scheme. I don't really want to have to open the amp up anymore after this is done.

On a positive note, I jammed on the amp yesterday and holy smoke it sounds good. I think the 32/32uf cap can really helps the vintage vibe of the amp. And I am surprised at the tonal differences available through the different input jacks. I will post up final pictures when I get the rest of the amp worked out.

for your help neikeel. Getting that rectifier circuit worked out was critical.

[marshallnoise]

Well, spent way too much time last night with the amp. Drilled 5 holes and repurposed one for the Larry grounding method. I also inserted 600v wire where higher voltages are present. Regrounded the whole amp. And I still have transformer hum that goes away when I touch the chassis. I will be doing some more research. Thinking I might need to isolate the transformer from the chassis somehow. Or it could be the way the full wave bridge rectifier is grounded.

[marshallnoise]

I am using an old 12AX7 that could be the source of my issues. It could be the wiring in my wall too. It could be ungrounded. It was too late last night and I am still too freaking tired right now.

All I know is that the hum goes away by touching the chassis and it gets louder when the volume is increased on either channel and no cable is plugged in to the input jacks.

/rant

[marshallnoise]

I have narrowed down the one point where the hum is coming from.



Its right on the south side of the mixer resistors that go to pin 2 of V2. Per the sleuthing of the guy in this (http://vintageamps.com/plexiboard/viewt ... 8&start=30) thread, I did similar testing. V2 is the culprit. Swapping tubes in does not change the situation. The sockets appear to be ok (I should order new ones anyway). The solder jobs are fine. The 470k resistors check out just fine.

From the thread mentioned above.

I took off all the pots, cleaned, and retightened. Checked all the other grounds I could find: main cap cans, power tube sockets, bias supply, presence cap, V1 and V2 cathodes. Pretty sure this has nothing to do with the input stage since I get the buzz even with V1 removed, and shorting the inputs and the volumes to ground does not stop the buzz.

Here is what DOES stop the buzz: shorting V2 grid to ground, or shorting the treble pot input to ground. But shorting the normal and bright pot wipers to ground does NOT stop the buzz. Based on my limited understanding of this circuit, that really makes it seem like the buzz is being generated inside V2 ? But I've tried four different tubes in there, with no change.

So, my best guess is that V2 is amplifying some noise that's being generated by some other failing component. Does that make sense ? Anyone have a good suggestion for what component that might be (given I've already tried replacing the preamp cap can). I'm assuming since removing V2 stops the buzz, it's not a power supply issue, but maybe it's still possible one of the main filter caps (brand new) could be causing this ?

One other potential clue: I heard no difference in buzz/hum with the preamp filter cap removed. Maybe that's because the buzz I've already got is drowning out the small amount being filtered by that can ? Just thought I'd mention, in case it rings a bell for anyone.

When I ground pin 2 of V2, the hum goes away (dead silent). When I ground where the red arrows are (anywhere where they are), the hum goes away. The volume knobs are new and are 1K. When I ground anywhere between the mixer resistors and the volume pots, the hum is still there.

Would it be beneficial to isolate the pots from the chassis with a cloth or plastic washer?

I am baffled at this point.



Edit: Here is another fella who had similar issues. http://forum.metroamp.com/viewtopic.php?f=3&t=23720

And a solution:

you'd only ever want to use shielded cable on the grid connections in the preamp, so voltage rating isn't really an issue as you won't get any major voltage on the preamp grids.

I use shielded single core wire from Bluebell Audio in Scotland, though I'm sure our hosts here probably sell stuff very much the same.

Shielded wire, here I come.

[marshallnoise]

I shielded all of the grids on V1 and V2 plus the inputs. Lots of noise has been removed. I also reran the heater wiring with new wire with the typical black/red combination. No new noises.

But I still have what I think is 60 cycle hum. It doesn't get louder with the volume pots and my touch of the chassis or anything metal when having a guitar plugged in stops the hum. I am wondering if I don't have enough filtration on the mains. I have two 50/50uf capacitors filtering the power supply. The other cap can is a 32/32uf can that is going to the big 2 watt resistors.

Any thoughts?

[marshallnoise]

Its definitely not a heater problem. I tried elevating the heaters to pin 8 of V3. No difference between that and grounding it at Larry grounding point 1.

I swapped out the middle wire on the volume pots for shielded wire and yeah, it got cleaned up even more. But there is still an underlying what seems to me its a 60 cycle thing.

[marshallnoise]

Practically rewired the whole thing with the 600v wire from ValveStrom. Great wire by the way. Pretinned, etc. Plus he hooked me up on shipping.

After doing that, every solder joint was redone and a lot of my noise issues are gone.

I think I am going to look at the input jack wiring more carefully and also isolate (physically) the transformer from the chassis. I think the last of my hum issues are from the power transformer. The amp is dead quiet when in play mode and the volumes are up but with no input jack. Just the normal hiss.

[marshallnoise]

Just ran the amp without the power transformer bolted to the chassis. No change. Still buzz when fingers are off the strings or touching the chassis.

[marshallnoise]

I isolated and moved around the output transformer and it made no difference other than not transmitting some of the mechanical hum to the chassis that gets transmitted to the amp. I will eventually isolate it with bushings. I may replace the OT with a Classic Tone OT anyway. That should solidify the Marshall part of the conversion.

The other thing that I am going to do is figure out how to install a hum balance control on the heater wiring. I have been listening all around the web and the buzz I have is very similar to hum balancing that goes away with the install of a hum balance pot and the fine tuning it offers. Going to have to be next week though.

[neikeel]

Sorry you are working hard but barking up the wrong tree, if I had realised i would have counselled against some of these things.

You found the hum related to the channel mixer resistor area?

Before hum balance try measuring the voltage either side of the heater centre tap. If they are +/- 0.1v then do not bother.

I think that a ground loop is much more likely if touching the chassis or controls abolishes it.

Post a pic of your ground points.

[marshallnoise]

Thanks neikeel. I ordered the parts. They aren't very expensive. I am jonesing for the OT anyway.

I will take pictures when I am back from the mini vacation over the weekend.

[marshallnoise]

Most definitely, the mixer resistor area is where the source of all the amp's noise comes from. When I ground the amp from any part AFTER the resistors approaching the grids of V2, I stop the noise.

Would that mean that the grounding problem is from that point forward? When I pull V2, the noise stops.

Also, when the guitar cord is NOT plugged in, the noise stops. When it is plugged in, that is when the noise starts.

[neikeel]

Most definitely, the mixer resistor area is where the source of all the amp's noise comes from. When I ground the amp from any part AFTER the resistors approaching the grids of V2, I stop the noise.

Would that mean that the grounding problem is from that point forward? When I pull V2, the noise stops.

Also, when the guitar cord is NOT plugged in, the noise stops. When it is plugged in, that is when the noise starts.

Is one of your switchingjacks partly open circuit/high impedemce on the inputs, do you have the 1M resistors securely to ground?