[Hammarlund] Retubing an HQ-180

Fri, 29 Mar 2002 17:54:17 -0500

I totally agree with Glen...by re-tubing, you're opening up a whole new set
of potential problems all at once.

No two tubes are alike in respect to inter-electrode capacitance: this was
made PAINFULLY clear to me a couple of years ago when I experimented with
swapping LMO tubes in my Heathkit SB-300 (I was too lazy to re-calibrate the
dial setting---figured the "right" tube would do it FOR me automatically).

You would not BELIEVE the ranges experienced in final LMO
calibration---something like +/- about 10 KHz, dependent upon which tube I
plunked in (and yes, they were ALL the same tube type, too). Now, imagine
this same scenario, ALL AT ONCE with critically tuned stages like your
HQ-180's IF amp tubes & BFO. You'll be chasing your tail for days...

Get the picture...? If it ain't broke, DON'T fix it! And if you HAVE to fix
it, do it ONE STAGE AT A TIME...

~73~ Eddy VE3CUI - VE3XZ

---- Original Message -----
From: "Glen Zook" <[email protected]>
To: "Mike McCoy" <[email protected]>; <[email protected]>
Sent: Friday, March 29, 2002 10:37 AM
Subject: Re: [Hammarlund] Retubing an HQ-180

> I do not recommend completely "retubing" a receiver.
> For one thing, you may have to do a complete
> alignment, then have to do it again after the tubes
> "age" a bit.  Tubes last for years.
>
> The best "tube checker" is the receiver itself.  If
> the tube is functioning properly in the circuit, then
> there is no need to replace it.
>
> I do recommend having a set of "spares" just in case
> you do lose a tube.  But, to do a complete retubing of
> the receiver is, in my opinion, an expense that is not
> necessary.
>
> Glen, K9STH
>
>
> --- Mike McCoy <[email protected]> wrote:
> > I just had to replace the 12AU7 BFO-meter tube in my
> > active 180 (which I
> > stole from from an older retubed 180). Because I
> > needed to replace a tube
> > (and not having a tube tester to check the rest)
> > makes me think I might
> > want/need to completely retube it in the not too
> > distant future.
>
>
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