Kendrick Gusher Help (loooong) ....

[michael_C]

howdy y'all,
first post ... i really appreciate the opportunity.

amp in question is a mid 90's Kendrick Gusher (2x12, EL34's, reverb) i purchased amp around a year ago. amp soon developed this crazy oscillation that turned out to be the switch gerald uses to switch between cathode and fixed bias. replacing switch took care of oscillation which left me to really get my head and ears around what this amp could do (i'm a fooltime gigging/touring player and while i'm not able to work on my own amps i do know a little about them and have fairly decent ears)

the problem i'm having with this amp is when you start to overdrive it there's this grainy quality/distortion to amp's tone that's present, fairly obvious and just not pleasing at all. the harder you push amp the more obvious it becomes. my tech has looked at amp; all voltages are good, amp is stable and reliable. one friend i lent amp to hooked it up to a scope and told me amp is not oscillating and that this sound i'm describing is visible as a pointed peak not usually associated with a clipping tube amp (really technical huh?) he was talking that it might simply be inherit in amp's design. personaly i don't see how as this distortion is NOT a nice sound. sound quality occurs in any input, cathode or fixed bias, extra gain stage in or out. when you push amp it sounds muffled and flat (ie not very touch sensative).

i'm waiting for a hole in my schedule that would allow me to leave amp with someone. i've corresponded w/ gerald many times, mostly about oscillation problem, and feel it's a little useless as we're thousands of miles apart and i know if i push issue he'll want me to ship amp to him which i can't do now and i don't want to bug the guy. if i can't get a handle on this at home i think i'm touring through tejas in the spring and mebbe' i'll bring amp by then.

any leg-up, insight or suggestions would be oh so appreciated as this situation is becoming disheartening. i probably paid too much for this amp (which incidently is beautifuly made) but my instincts tell me it should sound killer. i mean this stuff isn't rocket science right?

thank you in advance for the help!
mike

[MWJB]

Did it only start doing this since the cathode/fixed bias switch was fixed? Did it sound different before the switch went south?

Do you recognise this distortion when playing the Gusher MP3 download on the Kendrick site? (just to eiminate the obvious thought that it's just not your kind of amp)

If it is that unpleasant a sound (like a malfunction) then it does seem unlikely that it is a quirk of the circuit.

"all voltages are good" is a little vague and doesn't really give away much that might help to pinpoint a problem.

Have you tried plug in/out alternatives in the first instance (tubes, spkr cab etc?).

The fairest thing would be to send it back to Kendrick. Any builder would prefer to have first crack at sorting a problem with their amp, otherwise you run the risk of 3rd parties fixing the things that ain't broke and it may take longer to get to square one.

[stokes]

Like MWJB says it is probably best to let Gerald look at it.But first I would try different tubes.What kind of tubes are in the amp? Are they biased properly?I have seen this symptom in various amps and have most times attributed it to the tubes,usually current production tubes.Doesnt seem to happen in high gain amps like Mesa's with current production tubes,but I have found that NOS tubes "smooth" out the harshness that a lot of current production tubes exhibit in Fender type amps.

[sportster4eva]

"one friend i lent amp to hooked it up to a scope and told me amp is not oscillating and that this sound i'm describing is visible as a pointed peak"


That might be a clue. Maybe the amp is only "conditionally" stable, or the elements inside the tubes are rattling. I am curious as to where this peak was seen in the circuit.
But again, the guys that replied are right about letting the builder have it to see what it is, unless you have a real good tech that you have access to. maybe you should try some good old production tubes in there first, like mr. Stokes suggests.

BTW... would you be the Mr. Stokes from R.A.T. and A.G.A. in past years. If so then Hi again! I was a frequent visitor there, but some of the regulars became rather intolerable..

[michael_C]

thanks for the suggestions ...

i did notice fizzyness pre- switch fix

tubes are biased properly.

difficult to tell listening to gusher clips on website but i think i do hear this quality in recorded clip which would give credance to the notion there's nothing wrong with amp. (i love eating my own words they're so spicey)

tubes seem fine and not particularly microphonic. if i were to try swapping tubes would y'all suggest preamp or output tubes? (output tubes are jj's, rectifier is a mullard, not sure about preamp tubes)

i think scope was hooked up to speaker out???

i'll get in touch with gerald about bringing amp by when i'm out that way next.

thank you again fellas',
mike

[stokes]

I have tried some JJ El34's and 6L6's some time ago,at a customers request and found them to be very harsh in a BF Twin (6l6's) and a 45watt Marshall (EL34's).Could it be you are experiencing the same?
To sportster-since I dont recognize the R.A.T or A.G.A.sites you mention,I would have to say no that is not me.

[sportster4eva]

No worries.. the a.g.a. I was referring to is a usenet group called alt.guitar.amps, and the other one was rec.audio.tubes. There was a pretty cool, technically savvy guy there by the name of S. Stokes.
Thanks for the reply,
Paul

[michael_C]

el34 options ......

been poking around a little looking at el34 options.

are the old mullards really worth the bread?

i have the opportunity to pick up a pair of mullards (double halos, matching date codes of xf2 B3L5) one has a broken guide pin. both test 7500 @ 42 ma. guy wants 150.00 for pair.

what's everyone's opinion on today's el34's?

best,
mike

[stokes]

Mullards are considered the "hoy grail" of El34's.Will they cure your problem?No way to tell,without trying.Its an expensive experiment.Better you should find somebody with a different pair of tubes to try out,even if they arent Mullards you can at least see if there is a change/improvement in the distortion quality.If there is,then you can at least have a little confidence spending $150 on tubes.Tone is a totally subjective thing,some people like the current production tubes and dont see a need to spend $150 on a pair of tubes,I happen to be a big fan of NOS tubes,as are a lot of the people I deal with,and would not hesitate to buy the Mullards.I have 2 pairs of JJ EL34's I got a few years ago to try out and will probably have them for a long time unless I give them away,to my ears they have a very harsh/brittle top end.I would suggest making sure the tubes are causing the unpleasant distortion quality you are hearing before spending a fortune in NOS tubes.I am inclined to think they will sound better,but without actually hearing your amp,nobody could say for sure.