Hi Gary
I have made quite a number of 6m amplifiers in the class (GU74s, GS35B,
GS31B, 4CXxxxxx etc) that you described and 2 with 8877's.
The socket will be fine, provided that it has a good fingerstock contact
around the majority of the grid there should be no issues at all. In fact
your socket looks rather better than mine in this respect. All you need is a
good low impedance connection from the grid to the chassis.
The chimney should also be ok but I personally would not use those HT
connections, remove them and put a strap around the whole anode. On 6m this
is arguably unnecessary but it is good VHF practice to do so.
You may like to look at link:
http://wd7s.home.att.net/gallery-2.htm
This amp is exemplary in it's construction and performance and can be copied
religiously without fear of failure!
Look at this link:
http://wd7s.home.att.net/gallery-1.htm
Interestingly this amp has a single connection on to the top of the anode,
so perhaps I am being cautious for no good reason. The main thing on 6m is
to keep the value of tune C as low as possible and the value of L1 and
resonance as high as possible. You are aiming to get an acceptably low
loaded Q on the tank circuit in order to minimise I^2R losses. Try to use
good quality blocking caps because the circulating currents will be higher
than in a typical HF amplifier.
The coil sizes used in the WD7S amplifier work perfectly with this class of
tube and I have used these coil dimensions with a number of tubes in this
output class, they all have similar output C and operating parameters.
The 8877 is a class act on 6m as my 181 DXCC's show, I am sure that you
heard me in the pileups:-)
Regards
Conrad G0RUZ
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]On
> Behalf Of Gary Mitchelson - N3JPU
> Sent: 23 May 2004 02:04
> To: Amps@contesting.com
> Subject: [Amps] 8877 Question
>
>
> I have been looking for a good quality 1KW class amp for 6M but so far no
> real luck (not interested in using 3-500's on 6 again).
>
> I do have a couple of nice 8877's and a bunch of parts from some Harris
> RF-354 HF amps I scrapped but had some questions on suitability of some of
> the parts for 50Mhz.
>
> 1) All the 6M 8877 amp designs I have seen use the SK2200 tube
> socket. What
> I have from the Harris amps are Johnson 122-247-202 sockets, they have a
> full 360 deg silver finger stock Grid Ring. Are there any issues
> with using
> this for 50Mhz?
>
> 2) The chimneys from this are made by Harris. They are not like
> the straight
> wall chimneys I have seen on 8877's, these have a 5" opening in
> the base and
> flair down to around the tube (the RF-354 uses a single muffin fan for the
> cooling, although they spin it at 11,000RPM !) I plan on using a quiet
> squirrel cage type of blower. Any problems with using a chimney of this
> design?
>
> 3) Lastly the Chimney has built in Plate connection made of silver finger
> stock. All the other designs I see use some sort of clamp around
> the plate.
> Any issues using this type of connection over the clamp?
>
> Links below are to some pictures of the socket and chimney.
>
> http://www.mitchelson.org/pages/images/Amp/Socket1.jpg
>
> http://www.mitchelson.org/pages/images/Amp/Socket2.jpg
>
>
> Gary Mitchelson
> N3JPU Montgomery Co. MD FM19
> http://www.mitchelson.org/
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|
