Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Latole on February 18, 2022, 03:35:05 am
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Hello,
A customer has just brought me a Randall LB103 head to repair.
I am looking for the schematic of this amp, I am unable to find it.
I just wrote to Randall.
Someone has this schematic ?
Thank you
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I did look into it , all I could find is the user manual, even used an alternative search engine.
Look in the left side there is a list of hosts of this engine under URL.
https://searx.space/
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Thank you, I found user manual too
I talk and wrote to Randall amp service in Canada.
I hope they will send me the schematic.
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Receive the answer; they don't have schematic :BangHead:
Could this be the reason why a new customer just brought me a Randal head that has been to the authorized service department twice, a big box that I won't name and the repair doesn't last.
I will try to do better
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answer; they don't have schematic
:cussing:
How are people supposed to fix their amps ?! Well it isn't impossible but the schematic does help a lot.
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Is that why the Service Center do not do a good job on the amp ?
I found intermittent heater supply on the four EL34
More coming.
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Only simple issues do not require schematics
The amp I'm talking about ;
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Looks to be a complex amp, lots of knobs, 2 boards!!
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Yes very complex with voltage regulators, Op Amps and 3 boards very hard to work on.
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I think I found and fixed the problem, (at least one problem ) time will confirm it, the amp is under test.
At first the amp was not playing, no sound, pilot lamp on
Observation: the 4 EL34 tubes were not lit and had no heater voltage. The preamp tubes; normal heater voltage
History summary;
The connector (photo yellow arrow) is intermittent on 6.3 VAC red and white wires and it comes from the connector itself; bad crimped wires?
I simply ran 2 new wires( black arrows at right ) from the 6.3 volt AC (see red arrow on the left on the pictures) to the sockets of the first EL34
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Seen like an easy fix! What else remains?
Is that connector(yellow arrow) soldered to the board or attached to a socket?
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Seen like an easy fix! What else remains?
Is that connector(yellow arrow) soldered to the board or attached to a socket?
Socket solder on the board
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Yes an easy fix after determining that the preamp lamps are DC powered and only the EL34's were 6.3 AC powered .
I don't want to cause a short circuit and have more problems.
And knowing that repairing the connector in a sustainable way was not an option.
Most of the time, to fix an amp is easy .....after you know what to do.
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Most of the time, to fix an amp is easy .....after you know what to do.
Yeah. That's why they pay you the big bux! :l2:
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Receive the answer; they don't have schematic
Some years ago I got a Fender Squier 10 at a Flea Market
The amp was working (only a blown fuse) but it had damaged Grill Cloth and 115V PT (Here we have 240V line)
I asked to the Fender Support for the schematic (as to put it in my archive, as I've the amp) but the answer was the same, we have no schematic (even now I don't know who really build the amp), however they sent to me a new 240V PT and a baffle with grill cloth and Fender Label all for free
Franco
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preamp lamps are DC
Is that to reduce noise/hum?
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...Fender Squier 10 ....we have no schematic ....
Internet does.
https://archive.org/details/squier-fender-sp-10-schematic_202010/mode/1up
Sells 2nd-hand for about $30 here.
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I apologize with Latole for the OT
Many Thanks PRR
At that time it was impossible to find one, or, at least, it was impossible for me :icon_biggrin:
I've just put a copy on my database
Thanks again
Franco
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preamp lamps are DC
Is that to reduce noise/hum?
Yes.
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...Fender Squier 10 ....we have no schematic ....
Internet does.
https://archive.org/details/squier-fender-sp-10-schematic_202010/mode/1up
Sells 2nd-hand for about $30 here.
Fender schematics are probably the easiest to get from several sources.
I've already seen that for recent amps, schematics may be less available or not yet published, maybe it was the case for this Squier 10 ?
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Randall LB103 ;
The power transformer seems to be underpowered. The voltage of the filaments without any EL34 tubes is 6.48 volts AC.
With the tubes, it drop to 5.65 volts AC
Amp made in China ........
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Amp made in China ........
Yay... :sleepy2:
There are still things to be noted there, I'm sure it isn't all that bad, is it ?
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Amp made in China ........
Yay... :sleepy2:
There are still things to be noted there, I'm sure it isn't all that bad, is it ?
Until it work , this amp may not worth to spend money for repair in 10 years
It go two times at a big service center with no success; repair do not last,
What thy do ? I don't know, I see not work on circuit and customer don't know
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customer don't know
I usually tell everything to the customer, what they should know, after all the item belongs to them, and it creates trust, explore in though all possibilities, list some options, include cost and benefit, tell the customer.
What thy do ?
That is a good question! If repairing is a no go, then salvage, reuse the cab, chassis, working parts, repurpose, build something durable and dependable. Get rid of the cheese cheap chingling disposable stuff !! I would !! If the fee is right !
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.... maybe it was the case for this Squier 10 ?
I really think that the amp is only labeled Fender but is build in China and bought there (by Fender that resells), like your Randall (?)
Franco
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customer don't know
I usually tell everything to the customer, what they should know, after all the item belongs to them, and it creates trust, explore in though all possibilities, list some options, include cost and benefit, tell the customer.
That is what I do too. And with pictures.
Many service big box don't tell, too many people between customer and tech ? . Or ( and ) the customer don't remember ?