Sorry, I forgot the decimal point in the spec for the green "min" grid LED.
It is set to come on at 0.2mA not 2.0mA.
On Mon, Apr 4, 2011 at 12:39 PM, damon stewart <wsmc551@gmail.com> wrote:
> Hi Sam,
>
> By the way, my original call was KB7FUT. Never could come up with any good
> phonetics that were appropriate for the radio :).
>
> As far as what the 8410 can do with a little tuning, I have a good idea
> ;). Last weekend I decided to pull the tube access plate and measure the
> filament voltage as close to the sockets as possible (J1 and J2 on the tube
> deck board). I measured 5.6 volts after about 5 min of warm up with the
> primary's on the 240 volt taps. This also gave me about 2860v for the HV no
> load and about 2550v at 1A. So I decided to try the 220 volt taps, this
> brought the filament voltage up to 6.1 volts with the amp warmed up at idle,
> well with in spec, and the HV to 3180v no load and about 2900v at about 1A.
> The filter bank is 9x 470uF 400v caps for a max working voltage of 3600v.
> Also with 18 amps of filament current there will be another slight voltage
> drop from the lead feeding from J1 and J2 to the tube sockets, maybe another
> 50 to 100mV. For my situation even though my mains are right at 239 to 241
> volts (no load) it appears the 220 volt taps may be closer to ideal then the
> 240 volt taps.
>
> The screen voltage on the early 8410s was set to 200 volts and later they
> bumped it up to 225 volts. Mine measured 227v. I tested the amp with the
> screen voltage at 235v and 250v but no higher. This is not a neutralized
> design and you could run in to stability issues if you push the gain up! As
> it is 28w in = 1500w out with the increased HV and 250v screen. Note, if
> you do adjust the screen you MUST re-adjust the G1 and G2 bias. This can be
> done through the USB port using a serial com program (I use Tera-Term with
> Win 7). At the factory they set G1 (intermediate bias) to 60mA and G2 (full
> bias) to 200mA. I'm still playing with the ideal settings here but I have
> G1 set to 80mA and G2 set to 250mA right now.
>
> So what will it do now? I have not tested it on all bands with the new
> settings yet, but on 20m from the factory on the 240v taps and 227v on the
> screen it would run 1500w out with 37w drive and 2200w with 60w drive. The
> grid was going in to saturation at 60 watts. Now with a few hundred extra
> volts on the plate, 250v on the screen and the 50mA of extra G2 bias the amp
> will run 2800 CW with about 60 watts drive. Its still starting to go in to
> saturation but the grid current is still very low. The green "min" grid LED
> is set to light at 2ma. I see it start to light at about 2300w out, I dont
> remember exactly what it was at 2800w out but I remember I wasn't
> concerned. The max Ip I remeber seeing was about 1.35 to 1.4A at that power
> level. Yes, there is probably more in it yet. This was as far as I was
> willing to take it but all the values where still well with in acceptable
> limits.
>
> I dont recommend anyone changing the values from the factory. The amp runs
> very well as it is, I just wanted to see what it COULD do. Now I know and I
> dont plan on operating it at those levels. Its just nice to know.
>
> Damon Stewart, KJ7E
>
>
>
> On Mon, Apr 4, 2011 at 10:04 AM, Sam Carpenter <sam@owenscommunication.com
> > wrote:
>
>> It is a WAY cheaper foreign tube. I asked about getting one tubed in
>> EIMAC.
>> She said the difference was somewhere in the range of simply purchasing
>> the
>> EIMAC tubes. On that amp, the screen voltage is held way back and the way
>> things are set up, I don't see how you would run into grid problems on
>> either tube under 3k out. One tube 4cx1000 or 1500 could handle the rated
>> capacity of the amp in full duty cycle. It could also do it with low
>> drive.
>> I think they only run the screen voltage about 250v. If you upped that a
>> bit, you would have a 4k out amp. I don't know if the tank could take it
>> but
>> it looks like the PS would for casual use. I really like this amp.
>> Everything seems to be conservatively built and I like the 4cx1000
>> platform
>> because of the number of tubes out there. On top of that, there are two of
>> them. I do worry about the proprietary items that inevitably accompany the
>> newer amps. What chips will no longer be made, or whatever. Seems that
>> lifecycles are shorter all the time. That is what I love about the big
>> henry
>> amps. Excpepting the tank inductor. Most everthing else was off the shelf.
>>
>> Sam N9FUT
>>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
>> Behalf Of Damon Stewart
>> Sent: Monday, April 04, 2011 12:09 PM
>> To: amps@contesting.com
>> Subject: Re: [Amps] VTX-X118 Tetrode mytery tube?
>>
>> On 4/4/2011 1:38 AM, KL7RA wrote:
>> > Originally the new AP8410 used the Eimac 4CX1000A tubes but they made a
>> > switch to the VTX-X118. Seem to be a mystery tube, can't find the spec
>> sheet
>> > and never heard of them.
>> >
>> > Anyone know anything about this tube? My guess is Alpha used the
>> 4CX1000A
>> > but got them with a higher grid rating? It looks like this tube number
>> is
>> an Alpha
>> > part number to me.
>> >
>> > 73 Rich KL7RA Alpha amp owner
>> >
>> > > From Alpha:
>> > The amplifier uses the Alpha Power brand VTX-X118 tubes, a ceramic,
>> external-anode,
>> > indirectly heated tetrode that, unlike the excellent Eimac 4CX1000A,
>> is
>> qualified to handle
>> > the grid current that might be experienced in the AP8410.
>> > _______________________________________________
>> > Amps mailing list
>> > Amps@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/amps
>>
>> For what its worth. The most grid current I have ever seen out of my
>> 8410, even when testing its limits, has been less then 1mA. In the
>> serial data string the grid current is read in tenths of a mA. I
>> usually see somewhere in the 0.2mA to 0.5mA range with CW output well
>> over LL.
>>
>> From many of the reports I have seen and my own testing, the VTX-X118
>> seems to be a slightly improved Chinese version of the Eimac 4cx1000a.
>>
>> Damon Stewart, KJ7E
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>
>
> --
> Damon Stewart, KJ7E
>
>
--
Damon Stewart, KJ7E
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