Very trebly Dr Z Maz Senior 38w combo

[M Fowler]

A friend bought on Reverb a Dr Z combo in flight case Maz 38 Senior.

When he tried it he found it to have too much treble and not very interactive controls and I asked where he had the cut control which he responded at 10 but had noise on full clockwise rotation.

Cleaned pots, checked tubes all good, JJ's in preamp and power section. 68R cathode bias resistor 1k2 PI bias resistor. Tone stack is .1 and .047 I have to see what the treble cap is.

It does create some noise in the cut control slight hum. Tightened all the pots, jacks, and everything else I could get to.

The amp has a 120v fan attached with no grommet through the chassis so I put a grommet in, nothing like 120v on chassis from fan AC wires.

Any experience with this amp?

Mark

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[pompeiisneaks]

On facebook recently one of the techs that's a regular posted quite a bit about a Dr Z he did maintenance on. he also noted the 120V fan through chassis w/o grommet, as well as other things not done well,

His name is Lyle Caldwell, and his page is Psionic Audio, I did this FB search and you can see some of his notes on it:

https://www.facebook.com/search/str/psi ... rds_search

~Phil

[M Fowler]

I just saw this on Z-talk and Dr Z wasn't to happy about the bashing.

I thought the AC fan was an add on but now that I saw the FB post it does seem factory because I tried to lift the board and there is no way one could get to the AC wires to unsolder and feed fan AC wires through a grommet so I cut my grommet to make it work and that is what the FB guy did as well.

Mark

[pompeiisneaks]

I just saw this on Z-talk and Dr Z wasn't to happy about the bashing.

Yeah I think Lyle tends to be overly abusive with his comments. He's pretty damn smart, but most of his posts are extremely negative about how shitty someone else did their job and his is to constantly fix someone else's hack job.

I get that it's probably pretty frustrating dealing with some peoples messes, but that's pretty much par for the course with every job I've done, some people take pride in their work, and others don't, they get a job done at a minimum requirement level to get paid and move on. seems epidemic lately how much people want to trash talk on the internet.

~Phil

[M Fowler]

I don't understand the use of 3/8" pot holes but use short Alpha .25 pots. No locking washer, short threads and floating pot shaft in hole?

I go out of my way to buy correct sized pots which are 3/8" diameter thread with 3/8" long thread length to go through chassis and faceplate.

The grounding requires the pots to be tight on a Z.

Doc is too smart for me to bash but some things I wonder about from my experience keeping amps in stage use.
Right now I'm lucky if they go 6 months to a year.

Mark

[M Fowler]

If Lyle doesn't understand why many use 100R screen resistors then he needs to open his ears and eyes.

Mark

[thejaf]

Very trebly and not very active controls, I would suspect the "slope resistor" connections in the tone stack. Saw this once on a Budda Superdrive 80, just a bad solder joint but same exact symptoms.

[xtian]

Very trebly and not very active controls, I would suspect the "slope resistor" connections in the tone stack. Saw this once on a Budda Superdrive 80, just a bad solder joint but same exact symptoms.

Good idea. Easy enough to test by lifting the tone stack.

[JD0x0]

If Lyle doesn't understand why many use 100R screen resistors then he needs to open his ears and eyes.

Mark

I think he's well aware, but probably feels the slight tonal benefits of running 100R there doesn't outweigh the fact modern EL84's can be dicey and probably a bit safer with something like 470-1K ohms. It really depends on the design and operating points of the amp in question. If plates and screens are fairly low from the get-go, and the power tubes are known to be durable, then 100ohm screens would be fine. From what I understand, a decent percentage of guitar amps already run EL84's hard, and often will run EL84 plates over max rated spec.

OP: There's no pics of lead dress, but you definitely want to double check that, especially all the preamp dress.
Any 'bright caps' on the volume(s)?