Traynor YBA-1A...low distorted output.

[acorkos]

Traynor YBA-1A Bassmaster MkII....low distorted output. Replaced all tubes...no change. Checked all voltages....all check out as per schematic. Cleaned pots, jacks and tube sockets, and retensioned all tube sockets...still no change.

It sounds like when you have a fender amp with the speaker plug in the Ext. Speaker jack, or like an open power tube screen resistor. All resistors check out. The filter caps are original (1969)....if they were shot, wouldn't the voltages be off? I'm thinking I probably need to replace them.

Any ideas as to where I can look for the source of this problem? Thanks for your help.

http://www.schematicheaven.com/barga..._mkii_yba1.pdf

[Enzo]

OK, this amp also has the two speaker jacks like the Fender, so make sure you are not in the extension jack.

See the two surge arrestors in between the power tubes and the output transformer on the drawing? Try disconnecting them. Looks like two in series, so lifting one end of one of them should be enough.

But other than a lucky break like a bad surge limiter, approach this like any other amp.

What is your B+ at pin 3 AND pin 4 of each power tubes? What is the bias voltage at pin 5 on each power tube? Looks like you should see +537, +525, and -46. Those are ball parks from the schematic. What we don;t want to see is missing B+ on one pin, or bias that is substantially different between the sides.

Move to the phase inverter stage - you got about 240-250v on the two plates? Looks like the cathodes should be about 39v. The grids on each side ought to be something similar, 30-40 v. If the 39v is a lot lower, or one of the plate voltages is way high, then you have a dead side on your 12AX7.

And there are two more 12AX7s in the preamp. The voltages are on the schematic, so are they more or less similar on your amp?

There is your basic voltage check. If you did that, great, but make sure to do it right at the pins of all the tubes. You can;t check the screen voltage at one tube and decide it is OK for all of them.

Now do some signal path tests. if you have a scope, apply a steady signal to the input and scope stage to stage and see where it goes bad. otherwise try signal injection. Doesn;t matter what it is as long as you know how it should sound. I often just use hum.

Use a small screwdriver with an insulated handle, or just use your meter probe. Leave teh black probe not connected, so the red one acts more like an antenna, picking up hum in your area. Now youch your screwdriver or red probe to the grid of each power tube. Do you hear a hum from the speaker? Won;t be real loud, but you should hear it. DO both sides sound about the same? Does it sound like clear hum, or is the hum low and distorted too?

If that is OK< then touch the grid of the PI tube - looks like pin 7. SHould get a louder hum. is that clear hum or low and distorted? Turn the treble all thie way up, and touch either end of C4. Keep moving towards the input - pin 2 of V2, pin 7 of V2, tuern both volumes up and touch the plates of the V1. At each step, note if it sounds like clearly amplified hum of does it sound like the problem. By doing this, we hope to identify where in the process of the amp the problem lies. if you are unsure what it should sound like, try it on a working amp.

REmember this is a live circuit, so be careful probing.

You know what touching the tip of a guitar cord normally sounds like. This hum injection we are doing should sound similar. It would tend to be louder over by the input, because there is more amplifying stages for it to run through.

[acorkos]

See the two surge arrestors in between the power tubes and the output transformer on the drawing? Try disconnecting them. Looks like two in series, so lifting one end of one of them should be enough.

But other than a lucky break like a bad surge limiter, approach this like any other amp.

thanks for the reply, enzo. lucky break....it was an open surge limiter.

should i just remove them and leave them out, or if not, what do i replace them with? i've never seen anything that looks like these. they're brown rectangular boxes with leads on each end, one box longer than the other. one says: 1kv33 7a7 q, other says: 1kvs33 20a20 q. schematic shows one x 6rs20sp20b20, one x 6rs20sp7b7

would this work using standard diodes as replacements?.....

[Gtr_tech]

You didn't have an open diode, it was *shorted*.

The spike eater diodes don't really *need* to be there. They're put there to give voltage spikes created from overdriven output tubes somewhere to go without arcing the primary winding of the output xfmr or a tube socket. If you plan to run it balls out to get output section distortion, you may want them in there. If not, I wouldn't worry about it. I removed them from my YBA-3 'cause that beast will never get run past 2-3 on the master.

[52 Bill]

should i just remove them and leave them out, or if not, what do i replace them with?

If you review the schematics, they were removed from the circuit in later (1972) versions.

[Enzo]

I'm with those guys, if removing them solved the problem, leave them out.