Hello to the group!
Once again I need to impose upon the collective wisdom of this group
to keep from "reinventing the wheel" in respect to working on a friends
amp.
Here is the situation....
My friend has lent me an old Dentron GLA-1000 amp. (Yea, I know, it
isn't what I would call much of an amp either but it is in like new
condition and he bought it cheep about 3 years ago and hasn't used it
since. Sort of a waste.)
One of the little pieces of information that came with the manual
was an article out of Ham Radio magazine with regard to installing load
sharing resistors in the cathodes to prevent the catastrophic failure of
all of the tubes in the event that one went short. Seems reasonable so
far. The other note in the article is that the amp was designed for a
tube called a D-50 but 6LQ6 was a suitable substitute but, BUT, that
they would not work on 10 meters due to the inter electrode capacity
diferences...OK so far...
My question is how do I make 6LQ6's work in this amp? I know that
other sweep tube amps exist that either use 4ea 6LQ6 or similar tubes so
how come this one won't? (BTW it doesn't seem to work on 10 either and
I have checked to see if the mod was done to connect the tank circuit
up.)
My Second question.
There is reference to an update kit to put the input tuning network
in this amp as was done later in the "B" model. Obviously since Dentron
no longer exists, does anyone have a spare kit around or can provide the
component specs for the input tuning network on each of the 5 bands it
covers. I am assuming that we are talking about a pair of caps and a
tunable coil form of some type (Pi net) for each band.
If you happen to have the 5 coil forms available for a reasonable
price, please let me know what you want for them as I haven't seen any
out here at the swap meets in a LONG time. I'm not afraid of the work,
just need the parts.
If there are any other improvements that can be made to this little
amp that you are aware of and would care to pass along, they would be
greatly appreciated. I am doing these improvements to say thanks to my
friend for letting me use the amp for a while.
My observations of this amp gives me some ideas. Here are some
conclusions I have drawn so far...
The power transformer seems heavy enough to perhaps be used in a
voltage multiplier to incorporate some other more suitable type of
transmitting tube, say either a single 4CX400 or a 4CX800 maybe.
The tank components seem heavy enough to accommodate perhaps up to
800 watts or a bit more in a less than contest use amp...
With the high cost of sweep tubes ($30 or more each) and the cost of
a single 4CX400 by Svetlana at $130 and the 4CX800 at $190 plus $22 for
the socket these look like a possible alternative. Am I on to something
here or have I missed a better mod/rebuild? Perhaps a pair of 4CX250B's
with the G3SEK tetrode board?
Looking forward to your thoughts on the subject...
Mike Baker KØQZ/7
Peoria, Arizona.
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