Traynor YBA-1 Plate Voltage Problems

[Alistar]

So I switched the filters on this bugger to 32/32/16/16.  The EL34's look good, but the PI and Preamp plates are.. uh really low.
Those resistors are unchanged, but the voltage drop across them is very drastic: the voltages look good at the Filters, but after the plate resistors they are all <10v.

Also, the 4700/1W resistor SMOKES when I am testing the plate voltages. 

There has to be something I am overlooking.

[shooter]

The EL34's look good, but the PI and Preamp plates are.. uh really low.

since the 34's seem good, and they are the biggest current draw, normally, what happens when you pull all the other tubes?   

[Alistar]

I actually haven't pulled any preamp tubes yet, I'll try that tonite.
It is playable, though.  Doesn't sound all THAT bad, either!

I should probably post the remaining voltages on each tube, too, and double check with my back-up meter.

Is it advisible to replace a resistor (4.7k/1W) when you witness it smoking?

[sluckey]

Is it advisible to replace a resistor (4.7k/1W) when you witness it smoking?

Maybe. Depends on how much it's smoking and how damaged it is. It would be much more advisable to find out WHY it's smoking.

[Alistar]

Well, it only smokes when I use the DMM to check plate voltages on V1 and V2.
I don't know much about DMM workings, but if that 1W resistor is suddenly sizzling hot - I would think that the current through it has changed. 

[sluckey]

If the plate voltages of V1, V2, and V3 are all really less than 10v, then all 5 of those plate resistors should be smoking also. Check those voltages with another meter. What brand and model meter are you using?

Was the amp working before you replaced the filter caps?

[Alistar]

So I've been using a UEI DMM, maybe around 15 y/o - it does appear to be the primary culprit!
Attached are revised voltages, with a different meter. 

The voltages look like they are pretty close to where they should be.
I do have more questions, though.
- This amp was working, but with a bad bad hum.
   I replaced the filter capacitors ala JTM 45 [32/32/16/16]
   Changed to 1M volume pots
   V1a & V1b cathodes ala '1987 JMP Lead 50W EL34'

I have never personally played any Marshall other than some sort of JCM800 a time or two, so I'm not sure what to expect, nor did I get to do much with the YBA-1 beforehand as it was operating poorly.
     - It does not seem very 'loud', particularly vs AB763 - which I am aware is a different beast all together.
     - Zero 'clean tone' - the distortion is really nice, but both channels do not clean up at low volume -
     - 'farty' lows - (which, to my understanding may be related to the lower-value Filter Caps.)  Sounds ok with bass @ '0', but I think
         that is normal for the JTM45.

Perhaps, this is typical for this type of setup?
Other than being not that loud, its dead silent, zero hum, seems to play well, and the tone controls operate appropriately. 
I could post audio if that would help anyone.
   
     Also - suggestions for getting the upper mids/highs to cut a bit more?
     Is there any way to get some amount of clean tone out of this at lower volume settings?

Thank you all for your input!

[shooter]

Was the amp working before you replaced the filter caps?

?

[Alistar]

I should have been more clear in my response
When I got it, it powered up and everything, but had a severe hum: hence FC replacement.

- This amp was working, but with a bad bad hum.
   I replaced the filter capacitors ala JTM 45 [32/32/16/16]
   Changed to 1M volume pots
   V1a & V1b cathodes ala '1987 JMP Lead 50W EL34' 

I have not played a properly operating YBA-1, or JTM45 - but at full volume you could have a loud conversation over this one.

Beyond finding voltages and tracing signal path, I'm not sure how to trouble-shoot 'low-volume'.  I will start a search in this forum b/c it surely has been addressed previously.

Many Thanks!

[Alistar]

So, plugging along on the low-volume issue, I found the following page at geofex.
Time to start scratching some of these off of the list!

http://www.geofex.com/ampdbug/lowpower.htm

Faulty Preamp Tube
Faulty Power Tube(s)
Bad preamp cathode resistor
    An unbypassed cathode resistor has drifted upwards (to 5K-10K or over)
Faulty phase inverter
    If for some reason the phase inverter input side is good but the inverted side is bad, the power amp will still work, but power will be very low. This can be a bad 1/2 tube, a faulty socket contact, a broken or open plate resistor or coupling capacitor to the output tube, or a bad solder joint on any of these.
Open cathode bypass capacitors in preamp
Faulty vibrato circuit on neon/LDR vibrato Fenders
High voltage isn't high enough for some reason

    Failing rectifier tube - try swapping in another one
    Failing power filter capacitors
    Failing or open series dropping resistor in the bypass networks leading to preamp stages
    Failing bypass capacitor - treat as in power filter caps.

Open screen resistors on power tubes

[shooter]

Time to start scratching some of these off of the list!

You get through that list and i'll bet you're jamming!