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[KL7AM]

I have a 2000A with a bad Power transformer. Open Primary, so need a replacement or a repair.

Open to ideas!

Marty
KL7AM

[K6AER]

Well...

First, I would call ACOM.

Jay at array solutions repairs ACOM amps.

Tranix in Colorado Springs supplied the transformers for Alpha Amplifier. You could give them a try.


Once the transformers have been chemically bonded thay are not repaiable.

[KD6VXI]

I bet it's the screen voltage eh?  That's the shorted winding?

Common problem with those amps.

--Shane
WP2ASS / ex KD6VXI

[N4PY]

DXEngineering sells them.

[VE7RF]

I bet it's the screen voltage eh?  That's the shorted winding?

Common problem with those amps.

--Shane
WP2ASS / ex KD6VXI

He stated the PRIMARY has gone open.  You can get replacement xfmrs from Acom directly, or Array solutions, or DXE, or island amp repair in W6 land. (islandamplifier.com).   Bring lotsa $$$.

DXE, array solutions, and island amplifier are all authorized acom repair facilities.

[KD6VXI]

I bet it's the screen voltage eh?  That's the shorted winding?

Common problem with those amps.

--Shane
WP2ASS / ex KD6VXI

He stated the PRIMARY has gone open.  You can get replacement xfmrs from Acom directly, or Array solutions, or DXE, or island amp repair in W6 land. (islandamplifier.com).   Bring lotsa $$$.

DXE, array solutions, and island amplifier are all authorized acom repair facilities.

Missed that.

--Shane
WP2ASS / ex KD6VXI

[VR2AX]

Why do they fail to the point of having dealers stock replacement, is it bad usage, or bad product to start?

[AE0Q]

I bet it's the screen voltage eh?  That's the shorted winding?
Common problem with those amps.

When the screen voltage fails in an amp using GU74b tubes, it isn't the transformer, it's a tube shorting the screen to HV internally in a tube.

[KD6VXI]

I bet it's the screen voltage eh?  That's the shorted winding?
Common problem with those amps.

When the screen voltage fails in an amp using GU74b tubes, it isn't the transformer, it's a tube shorting the screen to HV internally in a tube.

While I agree that nearly all the failure modes are thus, a 1 ohm resistor would be a cheap fuse.

The Gu74 is a sh1t tube. 

--Shane
WP2ASS / ex KD6VXI

[VR2AX]

Why not a separate screen voltage transformer. No power just voltage conversion. Did the real PWD make a replacement?

[KL7AM]

Turned out to be the power transformer was fine. Had a bad 47 ohm resistor in the step start circuit and also two shorted 1n4002's and a open trace on the low voltage PS board.

I got the amp partially disassembled from an estate. in the estate was a bad LV transformer and a bad LV PS board that probably came out of the amp originally. Also included was a new replacement LV Transformer and the replacement LV board which I repaired.
The SK op had much trouble with RF gear..

Works GREAT now!

[K6OK]

Tranix in Colorado Springs supplied the transformers for Alpha Amplifier. You could give them a try.

* Tranex.   Google and Wayback suggests that Tranex no longer exists.  It appears they might have been merged into or became Badger Magnetics in Minnesota.  https://www.badgermagnetics.com/

[W2NO]

You can get a Transformer directly from Acom in Bulgaria. You will not find a cheaper one anywhere.

[K0AP]

I bet it's the screen voltage eh?  That's the shorted winding?
Common problem with those amps.

When the screen voltage fails in an amp using GU74b tubes, it isn't the transformer, it's a tube shorting the screen to HV internally in a tube.

While I agree that nearly all the failure modes are thus, a 1 ohm resistor would be a cheap fuse.

The Gu74 is a sh1t tube. 

--Shane
WP2ASS / ex KD6VXI

Both of my amps use GU74b's and no problems whatsoever. Great tube... otherwise, ACOM would not be selling thousands of 2000A's and 1000's.
Last year replaced the GU74b in my ACOM 1000 after 20 years of service on the original tube. By which standard is this a sh1t tube? Plus, relatively cheap to replace, compared to some other valves. I am extremely happy with my ETO 91b and ACOM 1000. Very reliable, trouble-free amps.

73 Dragan K0AP

[AE0Q]

Both of my amps use GU74b's and no problems whatsoever. Great tube... otherwise, ACOM would not be selling thousands of 2000A's and 1000's.
Last year replaced the GU74b in my ACOM 1000 after 20 years of service on the original tube. By which standard is this a sh1t tube? Plus, relatively cheap to replace, compared to some other valves. I am extremely happy with my ETO 91b and ACOM 1000. Very reliable, trouble-free amps.

When they DO fail, the GU74b shorts the screen to HV internally.  This is almost always catastrophic for some of the screen supply parts.  I have repaired hundreds of Alpha 91B and 99 amps with screen parts incinerated, the FET regulator blown apart or shorted and resistors blown open.  Acom built all 900 of the 91B amps using metal film and/or carbon comp resistors in two places that get overloaded by the tube shorts, the resistors get red hot instead of opening.  When the 91B amps started coming in with PC boards with big black holes burned thru, Alpha started changing those 2 parts to metal oxide flameproof resistors on all the new 91B amps shipped from Mead, Colorado.
Maybe Acom uses a different circuit now...
Glenn AE0Q