Hi David,
Another project I see. :>)
Are you changing the load control as well as the plate tune control to
obtain maximum output when tuning the amp?
The first thing that I would do is open the meter circuit leg and place
another known good ammeter in series with the existing meter and shunt.
Often on old gear I have found that the meter shunt resistor goes high and
it looks like you have more plate current than you really have.
Also check the plate voltage under load. There are two voltage doubler
circuits in there and part of one can quite and you still get some plate
voltage.
Check the screen voltage too.
Check the resistance of the input load resistor bank. I think that it is
supposed to be 75 ohms. Someone may have put in different resistors to make
it 50 ohms or whatever, to use it with a higher powered driver. That would
kill some of the drive as the SBE33 is usually short on output on a good
day.
When tuning an amp with the SBE33, I used to use the driver tune control to
control drive level for tune up because when the SBE33 is placed in the tune
position it supplies full output all the time. By detuning the driver tune
control you can vary the output up and down so you don't cook the amp tubes
while tuning.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of David C. Hallam
> Sent: Thursday, November 26, 2009 8:56 AM
> To: AMPS List; ham_amplifiers@yahoogroups.com
> Subject: [Amps] Sweep Tube Amp
>
> I recently acquired a sweep tube amp and I got it for nostalgic reasons.
> This is my first experience with one of these beasts. It is the
> Side Band Engineers matching amp for an SBE-33 which was first phone rig
> I bought after I got my general class in 1964.
>
> Anyway, I had to do some work on it before trying to put it on the air.
> It uses 6 - 6JE6's. I see that 6LQ6's are often shown as
> interchangeable. The amp came with 5 - 6JE6 and 1 - 6LQ6. Are they
> really mixable?
>
> The output is very low. With a single tone drive, it loads to 1.2 amp
> which is spec and seems to be peak output point too. However, the
> output is only about 150W. Is the tube mixture a problem or are all the
> tubes just soft or both? I shudder when I see the price of 6 - 6JE6's.
> Of course, the manual says to use matched sets which is probably
> impossible these days.
>
> David
> KW4DH
> --
>
> "A democracy cannot exist as a permanent form of government. It can
> exist only until the voters discover they can vote themselves largess
> out of the public treasury. From that moment on, the majority always
> votes for the candidate promising the most benefits from the public
> treasury, with the result that democracy always collapses over a loose
> fiscal policy, always to be followed by a dictatorship."
>
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