Never worked on one of these before, thought I would share. Gorgeous build, just wish they wouldn't have potted any electrolytics... Maybe I can still return them to the factory for replacement.
"For simplicity of maintenance, the pre-amplifier is divided into several encapsulated modules, each containing a separate circuit designated by color code and designed for rapid replacement.
Signal tracing methods may be used to isolate trouble in any one of the modules, which may then be replaced without time consuming voltage and component tests.
The following is a module description and color code. The blue modules are high impedance input amplifiers. The green module is an interstage mixer amplifier. The yellow is the reverberation amplifier, and the red module is the tremolo oscillator and modulator.
Defective modules should be returned to the factory for replacement."
Standel SS amp
Moderators: pompeiisneaks, Colossal
Standel SS amp
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Re: Standel SS amp
Wow, that is Hiwatt levels of tidy. I'm impressed. Looks like they have schematics for the modules up on their site.
https://standelamps.com/schematics/
https://standelamps.com/schematics/
Re: Standel SS amp
Thanks! Already found the site, that's where the quote is from. The irony of "simplicity of maintenance" in unnecessarily potted blocks is reminiscent of some current anti right to repair tactics. Luckily the epoxy machines rather easily, not too chippy, but cutting into an opaque block with a dremel and not knowing exactly where anything is truly sucks. These blocks also don't seem to be exact matches of the schematics...alnight wrote: ↑Mon Mar 17, 2025 10:19 pm Looks like they have schematics for the modules up on their site.
https://standelamps.com/schematics/
Re: Standel SS amp
Well, I know I didn't get everything, but further attempts would likely be destructive and overly time consuming. Schematics do not match the potted modules so I would be dremmeling blind and uncertain if there are more electrolytics. They are on PCBs, so coming from behind is very difficult, and they appear to have filled some voids with hardboard to save epoxy so excavating from the top is also a pain... It's working and sounds pretty good, think I'm done.
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Re: Standel SS amp
Yeah, those are PITA to work on. Back in the 1980's, when I was in high school, we'd get those relatively regularly in the shop I worked in.
There were no replacement modules and no information about how they worked or troubleshoot them.
The modules are literally plastic jewel cases, like fishing lures used to come in. Drop the circuit in them, then dump the epoxy in. The epoxy is the tough, hard kind.
We were sometimes able to use a Dremel to cut into the modules and do repairs, usually from the bottom, so it is easier to get to the boards, if they used them, and figure them out. Lot of work and not worth it.
That one is one of the nicer looking Standels. Many of them were not that clean inside in my recollection.
There were no replacement modules and no information about how they worked or troubleshoot them.
The modules are literally plastic jewel cases, like fishing lures used to come in. Drop the circuit in them, then dump the epoxy in. The epoxy is the tough, hard kind.
We were sometimes able to use a Dremel to cut into the modules and do repairs, usually from the bottom, so it is easier to get to the boards, if they used them, and figure them out. Lot of work and not worth it.
That one is one of the nicer looking Standels. Many of them were not that clean inside in my recollection.
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Stevem
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Re: Standel SS amp
One of the failure points of these amps is that the potted transistors can't breath .
The epoxy acts like a insulator .
I see this type of failure a lot here at work when a transistor is bening run close to its limit.
Transistors put in with unnecessarily short leads can't long term disappate heat as needed and break down.
The spec's listed of wattage in a spec sheet are for uncut lead length, and the leads act as heat sinks.
As this photo shows there's no need to put transistors in with more then 1/2 there lead lenght missing when there's 2" of head room above them.
The epoxy acts like a insulator .
I see this type of failure a lot here at work when a transistor is bening run close to its limit.
Transistors put in with unnecessarily short leads can't long term disappate heat as needed and break down.
The spec's listed of wattage in a spec sheet are for uncut lead length, and the leads act as heat sinks.
As this photo shows there's no need to put transistors in with more then 1/2 there lead lenght missing when there's 2" of head room above them.
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When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Standel SS amp
I worked on those amps back in the early '70s! The modules were still available for them back then, and they got replaced quite a bit. I can't remember what we paid for them, but I don't think it was a lot; maybe $10 or so?
Those jewel boxes they were potted in were actually the plastic retail cases (usually fixed to a cardboard hanging card) that carbon film resistors and smaller value capacitors were sold in back in the day (Sprague, I think?). They obviously had a "waste not, want not" ethic going back then, and recycled these into their modules.
IIRC, it was usually the blue preamp modules that failed, with the occasional green mixer module going on the fritz as well.
Those jewel boxes they were potted in were actually the plastic retail cases (usually fixed to a cardboard hanging card) that carbon film resistors and smaller value capacitors were sold in back in the day (Sprague, I think?). They obviously had a "waste not, want not" ethic going back then, and recycled these into their modules.
IIRC, it was usually the blue preamp modules that failed, with the occasional green mixer module going on the fritz as well.