| Schematic Needed for Kustom L795RV [message #29548] |
Mon, 12 May 2025 03:07  |
EasyGoing1
Messages: 7
Registered: May 2025
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Junior Member |
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A friend of mine has a Kustom L795RV and the output jack that I assume would go to the speakers had some "custom changes" done to it inside the case, and we're trying to figure out where those wires originally connected to. If anyone has a schematic for this unit, it would be helpful.
Also, being as old as this unit is (1966 from what I can figure out), I'm assuming that a proper rebuild will require the replacement of all electrolytic caps?
If someone has the schematics and they can't be posted here for whatever reason, my email address is: sims.mike@gmail.com
Thank you,
Mike
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| Re: Schematic Needed for Kustom L795RV [message #29551 is a reply to message #29548] |
Tue, 13 May 2025 07:49  |
stevem
Messages: 4863
Registered: June 2004
Location: NY
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Senior Member |
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Hello and welcome.
The schematic you need is in this site’s technical section on the home page.
Go to the listing for amps and then down to the K200 listing.
There will be the whole schematic and also it broken down into more viewable sections.
First off while working on the amp I would detate the main fuse from 3 amps down to 1.5 and the speaker fuse from 5 amps down to 1 amp unless you can afford to loose those speakers your listening thru.
Yes, all the electrolytic caps should get replaced .
The two big can type main power supply rail filters might still be good.
Also all the resistors on the output transistors should get replaced with 1% tolerance ones if you can find them .
The 1 ohm 5 watt and the 8.2 ohm are the most critical out of those 3 resistors that they be 1% .
I have seen a 25 watt gain in output when when out of tolerance resistors where replaced with good ones.
I would also up rate the two 5 watt resistors to 7 watt .
The main filter cans have a red plug on top or a small circular round spot that will swell up if the filter is bad, but it never hurts to check them with a ESR meter once you have discharged them.
Be careful with I301 in the shrink tubing on the reverb / tremolo board as they are near impossible to to find but from a donor amp, and making them up again by finding the needed solar cell is a dead end.
Note that too avoid spam and hackers on this site I have to approve five of your post before they will just load up to the site on there own.
Also photos can not be posted to this site, you need to post them else where with a link to them here.
[Updated on: Tue, 13 May 2025 08:16] Report message to a moderator |
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| Re: Schematic Needed for Kustom L795RV [message #29552 is a reply to message #29551] |
Tue, 13 May 2025 20:05 |
EasyGoing1
Messages: 7
Registered: May 2025
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Junior Member |
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Thanks for the detailed reply.
Looking at the schematic page, I see a lot of links to different K200 schematics. Any idea which one is the most accurate for the L795RV?
Also, since you've obviously been down this road a few times, do you have a general estimate on what it might cost for the parts? There are a lot of caps in this amp and I'm thinking they will be the most expensive portion in a rebuild.
The owner wants to fire it up before doing anything to it just to see if it works. I'm leaning towards NOT doing that in the interest of preventing more damage in case any of the caps are shorted or just any unknown in general, but I do understand him wanting to see if it's worth even throwing any money at it at all. It looks to me as though the unit sat outdoors for a long time based on how bad it looked on the inside before we cleaned it up, so there's really no telling what condition the components are in at this point.
The circuit boards look to me like they were chemically etched which I'm assuming was a common way to do things back in the 1960's.
Are those output transistors fairly resilient to time and use?
I took a couple years of electronics back in the early 90's in college and haven't really used that education much at all except in digital electronics and microcontrollers. My experience with analog audio electronics is basically nill in the way of circuit analysis and troubleshooting, but I've got good skills with a soldering iron and good equipment - a Weller station that set me back a few hundred (best iron I've ever had), I've also got a nice re-work station and even an ESR meter which I know how to use, so I'm not completely useless, but I'm certainly not what I would consider fully competent either.
Thanks again for your response and your time.
Mike
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| Re: Schematic Needed for Kustom J695RV [message #29553 is a reply to message #29551] |
Tue, 13 May 2025 21:31 |
schmittp
Messages: 4
Registered: May 2025
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Junior Member |
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First off, my apologies, I apparently messed up the model #, it is a J695RV.
I went to the page recommended, there is no K200 with no numbers or letters after, and most for the K200-x pages come up with: "Sorry, the file you have requested does not exist. Make sure that you have the correct URL and the file exists."
As a tech with> 50 years experience, I did replace the bad electrolytics that I found with my Sencore LC102 Z meter. I am not in the habit of replacing parts that are not bad.
As I mentioned in the post, I did not get the lamp part of the opto-coupler, and that is what the post is about, trying to find or create a replacement.
I had already determined that OEM replacements are N/L/A.
The coupler does not use a solar cell, it uses a photocell, different breed of cat. I was hoping someone who has a working one could measure the resistance of the lamp, and possibly the cell when the lamp is on. It would also be useful to know the voltage across the lamp when it is on, but one would need an analog meter to estimate the voltage, digital meters are useless with changing voltages. This information should be useful in determining what replacement parts should be chosen.
I guess I'm on my own to create a suitable replacement, but thank you for your response anyway. If I am successful, I will post my solution on your site, in the hopes it will help others.
Paul
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| Re: Schematic Needed for Kustom L795RV [message #29554 is a reply to message #29552] |
Wed, 14 May 2025 08:54 |
stevem
Messages: 4863
Registered: June 2004
Location: NY
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Senior Member |
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Schematic wise here’s a better explanation.
Go to technical.
Open the listing for models by amp.
Scroll down to the K200-A series.
That will have all the schematics.
The full schematic for that early model will have all the possible models/ circuit boards on it.
The different model numbers are just in reference to the boards used.
The basic amp was just two channels and no effects .
The PA head had reverb on just the left channel.
The guitar head had reverb and tremolo on the left channel.
These made up the three different model numbers.
The output section of these amps unlike the later B series amps had no short protection for the output transistors other then the 5 amp fuse.
The old way this amp has of driving and phase splitting done by the transformer method at least keeps 99 % of the problems on primary side of that transformer from effecting the output transistors.
That board on the rear wall of the amp that drives the transformer there next to it is also voltage regulator board for preamps making this a very high tech amp for its day !
These amps can have no signal output from one or both preamps just due to a shorted coupling cap that does not even look bad.
If the amp powers on without blowing any fuses then here’s what I would do.
Unsolder the gray wire going into the driver / PI board on the rear wall of the the amp and inject into to it a 1.5 volt audio test tone.
If all is well then you have at least confirmed that those two parts of the amp and the power supply are working.
The gray wires carry the audio signal into and out of the boards used in this amp.
I am concerned that you say the amp was filthy on the inside because if enough crap got into the control pots they may be unable to be flushed out without harm with out either taking them apart to do so or just replacing them.
If that driver / phase splitter transformer on the rear wall of the amp is bad then there’s no hope really of fixing the amp without sending that out to get rewound which is like a 250 buck deal.
Here’s the resistances to check to prove out that it’s ok with these wires unsoldered.
The resistance across the two primary wires should be about 9.7 ohms .
These amps tan to green and the brown to orange should both be about 6 ohms.
If none of these read open or under 5 ohms than the transformer is likely good.
[Updated on: Wed, 14 May 2025 08:59] Report message to a moderator |
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| Re: Schematic Needed for Kustom L795RV [message #29558 is a reply to message #29554] |
Thu, 15 May 2025 20:47 |
EasyGoing1
Messages: 7
Registered: May 2025
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Junior Member |
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stevem wrote on Wed, 14 May 2025 08:54
Schematic wise here’s a better explanation.
Go to technical.
Open the listing for models by amp.
Scroll down to the K200-A series.
That will have all the schematics.
The full schematic for that early model will have all the possible models/ circuit boards on it.
The different model numbers are just in reference to the boards used.
So I looked at the circuit boards in the unit, and I couldn't see any numbering on them, though it's difficult to get a good look at them because of the angles involved - without removing them from the case.
Can you tell by these photos which schematic I should use?
In the third picture, I put a red circle around the wire that we're trying to figure out where it needs to be soldered to. It's the wire that connects to the output jack. Right now, one of the blue wires comes from the fuse and is already connected to the jack so the wire thats hanging would be the wire that connects to wherever the output is from the output transistors.
...
Well, apparently I cannot put links in my posts until I have posted at least 10 messages, and I tried to just place the URL in the message but it wouldn't let me do that either, so unfortunately, you'll have to copy the links and paste them into your browsers address bar to see the photos.
i.imgur.com/cWzk2Ki.png
i.imgur.com/CG83YAV.jpg
i.imgur.com/N705htp.jpg
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| Re: Schematic Needed for Kustom L795RV [message #29560 is a reply to message #29548] |
Fri, 16 May 2025 13:18 |
stevem
Messages: 4863
Registered: June 2004
Location: NY
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Senior Member |
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The wire from the speaker fuse gets connected to where either the tan or green wire from the transformer goes to the output transistors.
I don’t have an amp here to look at, but here is what to look for.
If you look at the schematic you will see where one wire from the transformer connects to r8 r9 and r10.
That is where that speaker wire from the fuse connects to.
If your still confused pm me your email and I will send you a photo to guide you.
[Updated on: Fri, 16 May 2025 13:19] Report message to a moderator |
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| Re: Schematic Needed for Kustom L795RV [message #29563 is a reply to message #29548] |
Fri, 16 May 2025 19:01 |
stevem
Messages: 4863
Registered: June 2004
Location: NY
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Senior Member |
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When you open the list for the K200-A series the first schematic that loads up is the whole amp with all the possible circuit board / models on it that the amp could be made up with.
The next 5 schematics that are after that is that same schematic, but broken down into smaller easier to view sections.
If you scroll down more then a total of 6 schematics then your into the next amp series which is not what you have from what you have posted up.
Both preamp circuits are exactly the same in that amp and they are on one board.
Next on the rear wall of the amp there’s the board which is the preamp voltage regulator board and the driver to the small transformer.
Then if the amp has effects you have the other board which is either just reverb, or reverb and vibrato.
[Updated on: Fri, 16 May 2025 19:10] Report message to a moderator |
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| Re: Schematic Needed for Kustom L795RV [message #29565 is a reply to message #29560] |
Sat, 17 May 2025 00:53 |
EasyGoing1
Messages: 7
Registered: May 2025
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Junior Member |
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stevem wrote on Fri, 16 May 2025 13:18The wire from the speaker fuse gets connected to where either the tan or green wire from the transformer goes to the output transistors.
Here is a top view of the amp ... the red arrow is pointing to where I connected the output to, but the amp will turn on but no sound comes out... is this the right spot?
The brown arrow indicates where the "tan" wire goes to. I didn't try that spot yet.
Again, you'll have to copy and paste the link until I get to 10 posts where I can then post links into my messages.
Mike
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