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Trevor Wilson
Guest

Mon Jul 17, 2017 2:42 am   



On 17/07/2017 10:20 AM, Phil Allison wrote:
Quote:
Trevor Wilson wrote:
---------------------



No way, whatsoever were they SAFE to use in a SONAR test lab.


**YIKES!

Did you ever see any of the big Mike Davis designed EHT MOSFET amps?



** Yep - saw quite a few of them, EHT2000 and EHT4000 models.

I managed to get a loan of an early production example of a 2000 from the owner who worked for Etone at the time. The chief designer for Jands, Doug Ford and his production manager Terry popped over to see it too.

The use of standard aluminium extrusions and fan blowing the toroidals transformers was commented on favourably. Having reed relay current sensors in the speaker lines was novel as well.

The way the AC wiring was installed on top of the heatsinks using a PCB and large plastic bolts was slightly mind blowing. But the amps had a fatal flaw that turned up after a few years in use.

The fan blew directly onto the copper pattern of the power amps PCBs which were *NOT* coated to protect them from moisture and the corrosion that results. Also, the lack of thermal cut offs meant that if the heatsinks clogged with fluff or the fan stopped, the whole assembly cooked.

Dissasembly, full immersion cleaning and repair is a MASSIVE job that I have done a few times, but not happily.

Perreaux had a similar problem with lack of PCB coating - but was far easier to deal with. Failure to deal with it meant the amps blew up as "tracking" began between adjacent tracks that differed by 200VDC or so. At least Perreauxs all had DC rail fuses that saved the MOSFETS.


**Ouch. I'll ask Mike about those issues later today. He still keeps
musicians' hours (ie: He doesn't get out of bed 'till after 1:00PM).

--
Trevor Wilson
www.rageaudio.com.au


Guest

Mon Jan 22, 2018 11:58 am   



HI ~misfit~
I came across this thread in search for any information on the eht systems, I have 4x of the eht4000 amps an trying to find a path to the user manual. or even specs on the pmh3 and pmh2 speaker boxes. Do you have any leads online?

also built a playmaster pro3 in year 10 for my major electronics project, it is still alive and kicking nearly 14 years later!

~misfit~
Guest

Tue Jan 23, 2018 1:03 pm   



Once upon a time on usenet aaron.mcdonald7_at_bigpond.com wrote:
Quote:
HI ~misfit~
I came across this thread in search for any information on the eht
systems, I have 4x of the eht4000 amps an trying to find a path to
the user manual. or even specs on the pmh3 and pmh2 speaker boxes. Do
you have any leads online?

also built a playmaster pro3 in year 10 for my major electronics
project, it is still alive and kicking nearly 14 years later!


Hi Aaron.

Sorry I have no leads to give you but others here might. I've tweaked the
Playmaster Pro3, rewired the power supply, replaced the capacitors etc but
I'm still not happy with the sound so the case / heatsinks / toroids are
going to be used for another project I have going - one using K135 / J50s.

Good luck with your search.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

Trevor Wilson
Guest

Tue Jan 23, 2018 10:39 pm   



On 23/01/2018 10:03 PM, ~misfit~ wrote:
Quote:
Once upon a time on usenet aaron.mcdonald7_at_bigpond.com wrote:
HI ~misfit~
I came across this thread in search for any information on the eht
systems, I have 4x of the eht4000 amps an trying to find a path to
the user manual. or even specs on the pmh3 and pmh2 speaker boxes. Do
you have any leads online?

also built a playmaster pro3 in year 10 for my major electronics
project, it is still alive and kicking nearly 14 years later!

Hi Aaron.

Sorry I have no leads to give you but others here might. I've tweaked the
Playmaster Pro3, rewired the power supply, replaced the capacitors etc but
I'm still not happy with the sound so the case / heatsinks / toroids are
going to be used for another project I have going - one using K135 / J50s.

Good luck with your search.


**Of course you're not happy with the sound. Those old MOSFET kit amps
were shitful, horrible sounding things. Reliable, but crap sound. Worst
of all was the ETI 5000 amp. Find an old Phase Linear and you'll hear a
far superior sounding amp.

--
Trevor Wilson
www.rageaudio.com.au

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