| J 595 Comes to my shop.... [message #27335] |
Fri, 24 May 2019 20:36  |
DeadKoby
Messages: 35
Registered: August 2017
Location: Cleveland, OH
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Hi everyone... I just acquired in a lot of amps (auction) a J595 Charcoal and matching speaker. It's the 3 knob variety, which I assume is for bass. It appears to have all its original guts, and still works properly. As an amp tech, I'm wondering if I should go after it for a cap job, BUT since it's not high voltage, and there's no sign of issue, leave well enough alone.
Secondly, What's with the model number J 595? Everything else is a 200, 250, something like that. I know the "Franks" were the earlier ones (66-7) but that's about all I know.
All your electrons are belong to us.
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| Re: J 595 Comes to my shop.... [message #27336 is a reply to message #27335] |
Fri, 24 May 2019 22:00  |
JDinPA17603
Messages: 69
Registered: May 2018
Location: Lancaster, PA
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This is strange...
According to the '70 price list the 595 was a 100 series PA system. Don't see any mention of a J anywhere with it but who knows. Where J does get involved however the cab is listed as having 2 - 15" Jensen speakers and a horn...hmmm maybe Pleat or someone else can shed some light on that part of things. That being said the amp should have four channels with volume, bass, treble and reverb. The "original" 595 is listed as having a column with 4 - 8" speakers.
Far as caps go if no hum and no signs of deterioration I leave the main filter caps alone. The electrolytics on the driver/output board i almost always replace now because I had two amps out of three bite me shortly after leaving the bench.
John
Old Us Navy Vietnam Vet
Playing for my own enjoyment and irritation of the neighbors.
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| Re: J 595 Comes to my shop.... [message #27338 is a reply to message #27335] |
Sat, 25 May 2019 06:04 |
stevem
Messages: 4774
Registered: June 2004
Location: NY
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Senior Member |
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Kustom amps without effects where just guitar or bass heads, the speakers are what determines what the amp can be used with.
In your case the J means that speaker cabinet came fitted with Jensen speakers so it was ment for guitar use as the driver's where the top of Jensen 15" concert speaker line model C15L.
In terms of what stage of life the internals of the amp are at depends on how offen the amp was used!
Many times just from age no less just sitting around a few of the white cased Mallory caps that where used on the circuit board will be out right bad as in having one end blown open , or the case cracked, or they just may have drifted way off in value.
The amount the bias and load resistors may have drifted on the 4 output Transistors can have a huge effect on the amps power output!
The worst one of these I have ever had would only output 60 watts of clean power and once I replaced all of those resistors the amp then put out a respectable 92 watts of clean power.
The 2 main 75 volt filter cans may be well on the way out also!
I had some that where bad and showed no sign of blowing out the red expansion plug they have on the top yet when the amp was cranking the AC ripple voltage came up and the D.C. Voltage dropped off way more then it should for that amount of output stage load.
For any of these 64 to early 67 type Frank heads I highly recommend making and installing a Zobel network off of the output feed to the amps speaker jacks to better stablize the output load seen on these amps!
Just as a interesting side note I am currently working on a 1965 and early 66 model Frank ( I had never seen the guts in this era model before ). and these amps are only 25 watts , they use the very common for back then big value output coupling cap type output topology.
They even for then back have a regulator circuit and used Delco Auto radio type T03 transistor for the phase inverter transfomer driver and in the regulator circuit!.
Before I get these amps back into the owners hands I will draw up a schematic as I have been unable to turn one up, which sucks!
[Updated on: Sat, 25 May 2019 06:07] Report message to a moderator |
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| Re: J 595 Comes to my shop.... [message #27339 is a reply to message #27335] |
Sat, 25 May 2019 19:00 |
DeadKoby
Messages: 35
Registered: August 2017
Location: Cleveland, OH
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Cool... thanks for the info. I got the speaker cab checked out... The back was off, and all the screws gone when I got it.. BUT the speakers tested fine, and sound good. Everything inside appeared healthy to the eye, as I always look for popped or leaky caps, and take some temperature measurements when things are running. Routine re-cap + Resistor value check should be in order for something of this vintage, but it plays loud, clean, and even with its 2 prong cord, nearly NO potential to earth ground. With the switch left, I get 0v, and to the right, I get 0.7v. Usually when the filter caps get leaky these things want to give you a nice poke with the zap stick.
You can see my Youtube videos... I played a bass and guitar through it for a test... and I can't see anything that it needs, unless I'm going for preventative maintenance.
All your electrons are belong to us.
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| Re: J 595 Comes to my shop.... [message #27340 is a reply to message #27335] |
Sun, 26 May 2019 14:55 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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Congrats on the new baby!
The schematic is in the technical section, mislabeled as a K200A. There is a hand written note, "Wide Panel" on it.
The small pc board on the rear panel is the power amp driver circuit and the 24 volt regulator for the preamp power supply. The blue lytic cap on the board has been changed already, as that one is a very common driver circuit failure.
The dual pot on the treble control is an interesting take on the traditional tone controls. The second pot adds a sort of bright switch to the end of the rotation of the treble control. It adds in a bypass cap to the circuit that boosts the high frequencies and unfortunately the hiss as well.
Please note that until the metalfront 150/250 series amps, the high and low inputs on all Kustom amps were not gain labels but tone labels. The high input cut the low frequencies out of the input signal giving it a bright channel effect.
Just my 2 cents, change the power cord to a 3-wire and remove the line cap.
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