| Help with fixing Kustom L795RV [message #28847] |
Wed, 16 November 2022 18:59  |
Smilan
Messages: 3
Registered: November 2022
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Junior Member |
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Hi,
I have on the bench a Kustom L795RV that came to me disassembled with burnt resistors at the power amp.
I replaced the faulty resistors and installed new 2N3055 transistors.
Now there's no smoke.
The voltages from the PSU seems to be right.
But what is going on is that as soon as I'm turning the amp on the amp start to squeal and the bulb on the current limiter starting to light bright.
When I disconnected the driver regulator board and connected the signal generator straight to the primary side of the output transformer with the signal on the RED wire and the BLUE wire grounded I got an output signal on the speaker.
When I disconnected the preamp and fed it with 25DCV from external PSU I got output signal on the wire that goes to the driver regulator board.
So it seems like the problem is with this board.
I replaced the three electrolytics on the board and tested all the transistors outside of the board and everything tested good.
Since I don't have a schematic for the L795RV I worked with the "Ross organ amplifier schematic" that I found on EL34 website that is pretty much identical to the driver regulator board and the power section of the L795RV.
What else can I do to make this amp works?
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| Re: Help with fixing Kustom L795RV [message #28849 is a reply to message #28847] |
Thu, 17 November 2022 06:09  |
stevem
Messages: 4774
Registered: June 2004
Location: NY
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Senior Member |
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Also note that the small transformer on the driver/ reg board IS the phase splitter in this amp and here is how it should test out, who knows with the burnt up output stage parts the secondary side may be shorted or open .
The primary side should read out at some 9.7 ohms, and the red wire should have the power supply voltage going into it.
The tan and green wires are 5.9 ohms.
The brown and orange wires are 6.1 ohms.
Be sure to ohm test that these two windings are separate from each other.
Should the wires on the primary side happen to be reversed then that could be making the amp oscillate .
[Updated on: Thu, 17 November 2022 06:10] Report message to a moderator |
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| Re: Help with fixing Kustom L795RV [message #28854 is a reply to message #28847] |
Thu, 17 November 2022 12:43 |
stevem
Messages: 4774
Registered: June 2004
Location: NY
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Senior Member |
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One of these amps with the main rail filter cans in good condition will do about 88 to 90 watts RMS into a 4 ohm load.
That's the best I have ever seen from one of these.
With a 8 ohm load you will see about 1/2 that.
As I recall the last time I rebuilt one of those it made 17 volts, or 36 watts rms into a 8.2 ohm load.
I recall the factory wattage ratings being at 5% distortion.
I only drive these amps with -10 db, or about. .150 volts @ 1K because that's all that is needed to drive these and many many other amps of all makes to there maximum clipped output wattage.
Remember these amp where made to have enough preamp gain to deal with the weak single coil pickups of the day back then!
[Updated on: Thu, 17 November 2022 12:54] Report message to a moderator |
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