[Amps] Amp Supply LK-500ZBx 3-500z tube & cooling question

Carl km1h at jeremy.mv.com
Tue Jul 8 15:26:35 EDT 2014

----- Original Message ----- 
From: "KB8NTY" <kb8nty at wowway.com>
To: <amps at contesting.com>
Sent: Tuesday, July 08, 2014 3:09 PM
Subject: [Amps] Amp Supply LK-500ZBx 3-500z tube & cooling question

> Asking for more help please.
> My early Amp Supply LK-500ZB model has the letter X at the end, reading
> LK-500ZBx, The x is also included at the end of the three digit serial
> number 500x.
> Does anyone have any idea as to what the "X" suffix in my model number may
> regard.


> I have read up on some past history of the Amp Supply line and am aware of
> the changes within the same models and at times not documented.
> Possibly as a long shot someone who may have been associated with the
> company may have any insight to what the "x" in the LK-500ZB model may 
> refer
> to?
> In my researching of the LK-500ZB pictures found on line I see changes on
> the raised sub-chassis that the two 3-500z tubes mount on. Some have a
> series of holes along the top exterior side (closest to cabinet), some
> sub-chassis are open on that end. In my early model there are no holes at
> all on the sub-chassis, and the sub-chassis is complete, in other words 
> the
> end of the raised sub-chassis on the exterior side is all one piece down 
> to
> the bottom of amp chassis (closed, not open) like in other versions I have
> seen.

The later design cooled the tube pins a lot better.

> Upon reading of the overheating of the tube pins I guess Amp Supply had 
> made
> changes along the way by drilling holes on the top of the sub-chassis and
> leaving the side open, all for better cooling ventilation.
> My fan is mounted low in that a 1/4" or so is placed to blow down below 
> the
> sub-chassis, but I guess in this earlier version, they didn't leave the
> other end open and had no ventilation holes to help the air exit.
> I hate to do so but when I replace my power supply board upgrade, I am 
> going
> to carefully take the 500z tubes out and drill out some holes into the
> sub-chassis to allow for the air from fan to flow through and exit.
> I have also obtained a new ebmpapst 4600z fan, thinking I may secure it to
> the outside, side of the amp along with a speed control (as this fan 
> really
> spins fast) to help exhaust the air flow.

Use the 4600n fan in place of the original as suggested earlier. Use a 
switch and resistor to control the speed.
Unless youre contesting or using RTTY/digital modes, you dont need an 
additional fan.

> Speaking of the tubes....just by chance I had the top off and turned the
> lights off in shack to get a thrill of seeing the 500z tubes glow...Sadly 
> in
> one tube upon key down I observed a slight purple haze up near the top of
> tube right at the anode location. I mean slight...I would say 1/4 to 1/2
> inch at most. This presented itself upon key down.
> Upon my reading I have read of leaks, and sometimes gas from unused tubes. 
> I
> cannot say if the tubes were or were not used much as I only recently
> obtained the amp.
> My question; I am asking for advise from the groups knowledge as to what's
> the deal?
> Is my tube going to blow-up?
> If so is there a chance if it does will it affect or take out any other
> component's?
> Will it cause my other tube to blow?
> If I am to replace, can I still use it until it gets worse or should it be
> replaced ASAP?
> If I have to replace can I just replace that tube or should I be required 
> to
> purchase both say as in a matched set?
> These are Eimac's with date code of 8438
> Again this purple haze is only slight, only seen in the dark, is small in
> size 1/4 to 1/2" at most and is located right at the top of the tube.
> Power output don't seem to be affected at this time as I can obtain close
> to1400 watts at best with amp.

In very few words....use the amp at full power to regetter the tubes.


> Prior to replacing the P/S board upgrade I am going to snap photos and 
> post.
> Sorry for all the questions. Trying to learn here and appreciate your 
> valued
> contribution.
> Kind Regards...Ross KB8NTY
> http://www.rossradio.net


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