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
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
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