I grounded my grids separately to the existing ground posts that were around
the tube. I
did not use the socket hardware. The straps could have been slightly shorter if
I'd
drilled holes right near the grid pins.
I drive it with about 80 watts. I keep the grid current to about 210 ma and get
around
1300w on all bands except 10, where it is slightly lower. I kept the original
parasitic
suppressors -- the amp was unused and they were in good shape, of course!
I installed a transistor bias switch similar to the one in Measures' QSK
circuit in place
of the RL2-1 deal. This resulted in slightly less idling current which reduced
the gain a
bit. If I were an SSB operator I would probably replace the cathode zener diode
with a
lower voltage one for best IMD.
I use a vacuum relay and a reed relay for QSK following Measures' design.
This is simple
and it works IF you have an exciter with an appropriately timed amp keying
output, like
the K3. You need to make sure there is enough time before and after RF is
generated.
I also added a soft start but have an rc delay for it so that it takes about
half a second
to pull in. I have no idea if this is optimal, but it has to be better than one
that pulls
in too fast to hear!
I ended up with an additional 1000 pf of output capacity for efficient
operation on the
low end of 160. The fact that I needed so much makes me think there is not
enough
inductance, but fixing that would be more work than I feel like doing!
Finally, after convincing myself that the reason they say "never operate CW in
SSB mode"
is that the slow t/r relay is expected to hot-switch (that's why that little
spark gap is
there), I decided that it is safe to do so with the fast relays that I am
using. I've had
no problems in the several months that I've been using the amplifier (including
running
QSK a lot in this weekend's contest).
On 11/25/2011 12:54 PM, Carl wrote:
> I have a couple of problems with that link Jim, here me out and comments
> welcome by all.
>
> - With the grids directly grounded the tube gain increases and 100W drive
> will result in more power out depending upon the R of the original grid
> chokes. In a SB-220 this can be 100-200W more for instance since they are 26
> Ohms. More gain leads to more potential for instability as well as more
> stress on the transformer.
> I suggest leaving those input resistors in place as they will also improve
> IMD slightly.
>
> - Contrary to many beliefs not all GG amps are completely neutralized
> either. That is easy enough to test. On 10M the grid current peak, plate
> current dip and power out peak should all coincide at the same tuning
> position. If not, what a few claim as parasitics is simply a TGTP oscillator
> waiting to happen and it aint pretty folks.
>
> - Grounded grids should be grounded for RF, not a pretty photo. With an
> insulated washer between socket and chassis each tube is grounded by the
> screw head only ON TOP OF THE chassis...in the plate compartment... and
> elsewhere as well to multiple points below. Thats a big no no to anyone
> experienced with VHF amps as well as preventing oscillations in HF amps. If
> you really want a light show try that with a 4-1000A at 4-6KV!
> Ideally both tubes should go to a very low inductance single point ground
> but that is not possible in most multi tube 3-500 amps. Instead use a single
> ground right behind the center grid pin of each tube which would be the far
> left and far right in the photo.All 3 low inductance grid straps should be
> 3/8 to 1/2" copper strap. Remove the connections to the socket hardware.
>
> - Silver solder is fine if its the real stuff and not RatShak crap but the
> parasitic suppressors and copper lead should still have toothed ground lugs
> to that mounting plate plus soldered. There will be considerable thermal
> stress at those points.
>
> - The RH suppressor resistors look cooked and should have been measured. A
> better and much more reliable suppressor is the one Ive mentioned on here
> since the 90's (AMPS started in 96) and used long before that. A 50 Ohm 5W
> MOX from Mouser and a pair of 100pf/500V silver micas from the same place
> for each tube. Use the original coil or make an exact copy; place a coil and
> resistor in parallel but not connected and place a cap at both ends to
> connect them. The coil leads carry the RF (-; These can be built self
> supporting or on perf board or whatever is convenient; leave a bit of air
> under the coil and resistor. The capacitors cancel the slight XL of that big
> resistor.
>
> - Interesting comments about the self start and its also sort of sad that
> all the 3-500Z and larger Ameritron amps do the exact same thing. They also
> run the 3.500 filaments high in order to get "advertised" output with
> Chinese tubes and knowing very well tube life is seriously reduced to 2-3
> years.
>
> - The 1N5408 negative rail clamp is a good idea but JI vehemently opposed
> that idea every time I suggested it and claims the 1N4007 is better.
> Unfortunately Ive had his "expertly designed" amps in here several times for
> service with vaporized 1N4007's when a direct short is what they were
> supposed to do.
>
> Carl
> KM1H
>
>
>
> ----- Original Message -----
> From: "Jim W7RY"<jimw7ry@gmail.com>
> To: "David Jordan"<wa3gin@comcast.net>; "AMPS"<amps@contesting.com>;
> "Bruce Ferratt"<uglyatc@yahoo.com>
> Sent: Thursday, November 24, 2011 1:15 PM
> Subject: Re: [Amps] On Behalf of K4BOF
>
>
>> Here you go!
>>
>> http://www.w8ji.com/tl922_mods_parasitic.htm
>>
>> 73
>> Jim W7RY
>>
>>
>> --------------------------------------------------
>> From: "David Jordan"<wa3gin@comcast.net>
>> Sent: Thursday, November 24, 2011 6:20 AM
>> To: "AMPS"<amps@contesting.com>; "Bruce Ferratt"<uglyatc@yahoo.com>
>> Subject: [Amps] On Behalf of K4BOF
>>
>>> I am looking for some help with the RLM parasitic mods. I ordered parts
>>> from Mr. Measures and am seeking pictures of what they look like when
>>> completed. I am NOT looking for the newer style 'hairpin' type mod. Mr.
>>> Measures advises against this type of style due to harmonics. If anyone
>>> has a TL-922A amp with the mods and can send a decent set of pics, please
>>> let me know. Thank you! 73 Bruce K4BOF
>>>
>>>
>>> 73,
>>> Dave
>>> wa3gin
>>>
--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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