Crate Vintage Club 30 Oddity

[Flynscot]

Hello- this is my first post, so thanks for putting together the forum and for taking the time to consider my question.

I picked up a Crate VC3112 the other day purely as an impulse buy. Got it home and discovered it sounded pretty darn good, so of course I had to pull it apart and see what was in there.

It has some interesting things inside:

The output transformer may or may not be original. In fact it looks more like an older one ( will attempt to attach photos). Marked DF-226 with a paper wrapping.

Power Tubes are Mesa EL84 (blu).

Three of the preamp tubes are also Mesa 12ax7, with one being a Groove Tube, I think. At any rate, it's not a Mesa. The PI, tube, maybe?

Speaker has been replaced with a Mesa Black Shadow (Celestion) MC-90. A little buzzy/distorted on the low end. Old speaker? Tube issue? Cabinet vibration? Not sure.

Some of the wax around a couple of the caps is missing, leading me to think at least one might have been replaced.

At any rate, an interesting amp. So far I like.

What so you guys think about that output transformer? Original or vintage-type replacement?

Would there be any reason for the preamp tubes to be mismatched?

I really like this amp. Seems to be a good platform for further enhancement.

[Leo_Gnardo]

Woops, how did I miss this one? That OT is likely original. I was surprised first time I opened a Crate VT @ 1992 to find a paper-wrapped OT. But there it was. FWIW neither GT or Mesa make tubes. Test and relabel. Or... just relabel, so most likely they're Sovtek Russian imports. (And Sovtek isn't a Russian company but an American company that imports Russian tubes. It goes round and round and winds up here... in a couple of Russian tube factories.) Or possibly Chinese for the pre tubes. Look past the paint and compare the insides of the tube with known samples from various sources. At one time GT & Mesa sold EI pre tubes, early 90's. Some of those sounded a treat.

Of course it's a good idea to use speakers that appeal to your ear. Maybe that's why the Mesa Black Shadow is in there. No reason you can't put in whatever you'd like.

IMHO the best "mod" that can be done in the Crate Vintage line, is to locate the "bright" cap that's wired from hot to wiper on the volume pot, and clip it out. Ahh, what a relief! Lets the rest of the spectrum come through without annoying "nails on a chalkboard" tone.

Also doesn't hurt to set bias appropriately for the output tubes. There are 2 versions, one is self-biased (sky high) so you would have to up the value of the 10W resistor that sets this. IIRC the factory value was 62 ohms, you could go to 75 or 82. If it's the fixed-bias version, measure the bias current as-is, then evaluate & consider altering or adding a trim pot to the bias circuit.

After 20 years of being "also rans" the Vintage series Crates are starting to find some fans. One of my customers who has his "ears on" is very happy with his.

They ARE a pain to remove from the "box" and again to R&R the PC board.

[Flynscot]

Thanks for the reply!

Could I get your opinion concerning the speaker buzz?

It occurs only on the low end, with notes played on, say frets 1-5 of the E and A strings. A scratchy, almost-static, distinct buzz that sounds like the cone has debris trapped between it and the cab, or that the cone baffle is contacting the cab ( neither is true, as I pulled parts and checked ).

Tubes going? OT going?

[DonMoose]

It occurs only on the low end, with notes played on, say frets 1-5 of the E and A strings. A scratchy, almost-static, distinct buzz that sound like the cone has debris trapped between it and the cab, or that the cone baffle is contacting the cab ( neither is true, as I pulled parts and checked ).

If available, try another amp (not stacked on the VC's cabinet) into that speaker. Then the VC amp into a remote speaker. That other amp needn't be anything special - just have a 4- or 8-ohm speaker that's halfway decent, and have an output rating of at least 30W.

If not available, separate the amp and cap with a speaker extension cable - you may have to make one - and see where the noise goes.

Could be loose/rattling hardware, a reverb pan issue (VC30 has 'verb?), microphonic tube ... have you seen R G Keen's Tube Amp Debugging page on geofex.com?

Hope this helps!

[jaysg]

Fwiw, that is the original transformer set. The stock speaker was a Greenback style from Eminence. The Mesa//Celestion C90 is an odd choice, imo, but may work. Obeid Khan designed it.

From The Gear Page
http://www.thegearpage.net/board/showth ... st14477982

The OT had a mechanical rattle if I hammered the low E. If you unscrew it a little, there should be some padding in between it and the chassis. I added more and it helped.

[Flynscot]

If available, try another amp (not stacked on the VC's cabinet) into that speaker. Then the VC amp into a remote speaker. That other amp needn't be anything special - just have a 4- or 8-ohm speaker that's halfway decent, and have an output rating of at least 30W.

Done! Swapped everything per your suggestion, DM.

Vintage Club speaker and cab check out fine. The buzz was duplicated in the other combo amp's speakers (ran it into a 2x10 combo I have).

That narrows things down significantly.

Now, where to go?

Thanks for the troubleshooting link. Will check.

[Flynscot]

Fwiw, that is the original transformer set. The stock speaker was a Greenback style from Eminence. The Mesa//Celestion C90 is an odd choice, imo, but may work. Obeid Khan designed it.

From The Gear Page
http://www.thegearpage.net/board/showth ... st14477982

The OT had a mechanical rattle if I hammered the low E. If you unscrew it a little, there should be some padding in between it and the chassis. I added more and it helped.

Excellent. Thanks for the thread link.

Was your rattle audible through the speaker itself, or was is a chassis-like rattle?

[jaysg]

Was your rattle audible through the speaker itself, or was is a chassis-like rattle?

It was clearly mechanical. I isolated it by pushing on the OT with one hand while slamming the low E with the other....not really easy to do.

[Flynscot]

Mine's definitely not mechanical.

More of a fizz or buzz on low notes.

Ordered new power amp EL84 tubes yesterday. I'll start there and see how it goes.

[Leo_Gnardo]

Mine's definitely not mechanical.

More of a fizz or buzz on low notes.

Ordered new power amp EL84 tubes yesterday. I'll start there and see how it goes.

Clipping and/or parasitic oscillation "riding" those low notes. If you can watch the output on a scope, you'll see it right away. Although the model may mention "50" I doubt you'll see much more than 30W at clip and maybe less. Also EL84 tend to get rattly, and you might hear them shakin' their maracas along with your low notes.

[Phil_S]

I have a pair of EL84 that I keep around for "shop use." They buzz on the low A. Sometimes tubes have parts inside that rattle. Leo alludes to this.

[Flynscot]

Clipping and/or parasitic oscillation "riding" those low notes. If you can watch the output on a scope, you'll see it right away. Although the model may mention "50" I doubt you'll see much more than 30W at clip and maybe less. Also EL84 tend to get rattly, and you might hear them shakin' their maracas along with your low notes.

Ahh, yes. Makes sense. The power tubes in this amp lie in a horizontal array almost directly above, and pointing toward, the back of the speaker. I suspected something like this (or possibly the OT not seeing the input it likes). Hopefully new/different tubes will solve it.

This is the VC 30, btw. Which seems far more believable than the 50. I'm dubious as to the VC 50's claimed wattage. The two amps are the same, except mine (the 30) has cathode-based bias, where the 50 is fixed. I suspect that Crate biased the 50 hotter with fixed bias and used different speaker(s) to get the 50 "one louder" and claim higher output.

[Leo_Gnardo]

Ahh, yes. Makes sense. The power tubes in this amp lie in a horizontal array almost directly above, and pointing toward, the back of the speaker. I suspected something like this (or possibly the OT not seeing the input it likes). Hopefully new/different tubes will solve it.

This is the VC 30, btw. Which seems far more believable than the 50. I'm dubious as to the VC 50's claimed wattage. The two amps are the same, except mine (the 30) has cathode-based bias, where the 50 is fixed. I suspect that Crate biased the 50 hotter with fixed bias and used different speaker(s) to get the 50 "one louder" and claim higher output.

Just for fun one day I modified an amp to test bias methods with a switch to go from one type to the other. Measured lower wattage with the self-bias BUT could hardly tell them apart by ear.

The less the tubes heat (lower bias current) the longer they'll take to reach the jingle bell stage. There's the rub. With self bias, you have a selection of resistors, not so easy to "fine tune" bias current the way you can with fixed bias. Self-bias you can pick an Rk value that keeps you out of crossover distortion at clip, or the next higher Rk that gives you a little crossover distortion. Some people can hear the difference. You have to satisfy your own ears. Suffice it to say Crate's resistor typically allows much more bias current than necessary. If you could pick EL84's that were low on the emissivity scale, might get away with not having to replace the cathode R. When I order Ruby tested EL84 (and I get the EL84CZ which are JJ's), I ask for and get ones with a Pc rating of 16 to 22, very low, and they usually work fine in this kind of application.

[jaysg]

This is the VC 30, btw. Which seems far more believable than the 50. I'm dubious as to the VC 50's claimed wattage.

Well you should be. Obeid is sort of apologetic about the marketing claims. They're simply lies. Mine is good for about 20W clean with a new set of JJ's. That's a very good place to be...not AC30 territory though.

[Baxtercat]

Guy at work gave me the two EL-84 version. I take it to small gigs often, now that I found & fixed the broken input jack/board connex. New '84s really brought it back to life, btw.

Thxx for the vol. pot cap suggestion. I will likely do that to this one.