[Central-Electronics] CE 200V - Tubes
Jim candela
[email protected]
Sat, 21 Feb 2004 10:49:13 -0600
George,
I'd be curious what a 100V/200v looks like on AM. Below are some links to
my QRO 20A back in April last year. At that time I was limited to 12-13
watts AM before I started gain compression RF output (seen by non linear
trapezoid as 100% modulation was approached). I have since beefed up the
driver circuit (got it hotter, and re-did the bias using a LM317 as a CCS),
and I can now match those waveforms at 15-16 watts (depends on AC line
voltage). Below are some links of my scope patterns.
If this text email does a carriage return to the link, knocking off part of
the link, just type in the rest manually in IE.
Modulated Envelope:
http://pages.prodigy.net/jcandela/CentralElectronics20AModifications/12.5_Wa
tt_Carrier_100%25_Modulated.jpg
Trapezoid:
http://pages.prodigy.net/jcandela/CentralElectronics20AModifications/12.5_Wa
tt_Carrier_100%25_Modulated_Trapezoid.jpg
The reason I ask about the 100V is that with a 20A, when you insert
carrier, the carrier balance circuitry is disturbed such that audio feeding
the balanced modulator sees a different impedance depending on whether the
audio is positive, or negative going. The more carrier you insert the worse
the imbalance is. This works out to load the positive modulation more than
the negative. At a carrier control level of 7 or 8 on the knob, when running
AM, the positive modulation peak is attenuated 20-30% from the negative
peak. Since this is a SSB rig, exceeding 100% negative modulation results in
DSBRC, which sounds horrible on a AM receiver (unless a synchronous detector
is used). Here is a link of what this looks like:
over modulated envelope pattern:
http://pages.prodigy.net/jcandela/CentralElectronics20AModifications/12.5_Wa
tt_Carrier_130%25_Modulated.jpg
over modulated trapezoid pattern"
http://pages.prodigy.net/jcandela/CentralElectronics20AModifications/12.5_Wa
tt_Carrier_130%25_Modulated_Trapezoid.jpg
If the carrier control was dual gang, you could compensate for this by
loading the negative modulation at the same rate as the positive (1n34a in
series with the 2nd gang). Being lazy, and a cheapskate, I chose to add a
fixed resistor in series with a 1n34 diode that pretty much equalizes this
effect when the carrier control is at about 7-8. Since this is a 1K pot, it
works out that a 240 ohm resistor is about right to re-balance the +/-
modulation percentages. You can add this Resistor-diode at the rear audio
jack, or wire it into the mode switch ( a unused set of switch contacts
exist ). The Resistor-diode must however be removed when running SSB. The
scope pictures shown all are with the R-D compensating network in place. A
stock 20A without the R-D, figure maybe +60% modulation at -100% modulation
at 3 watts carrier output, worsening at 4 watts. Part of the trouble is the
RF stages are well into gain compression at anything > 3 watts RF carrier
output on AM. Running 2 watts out, or less does give decent AM however.
Compare that with the 15 watts I achieve with my QRO #2 20a, and the
difference is huge.
I kind of like tinkering with this old stuff. The designers were
significant pioneers in radio advancement.
Regards,
Jim
WD5JKO
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of George
Maier
Sent: Friday, February 20, 2004 8:06 PM
To: 'Jim Candela'; 'Radio Central Electronics'
Cc: 'Chuck Ochs'
Subject: RE: [Central-Electronics] CE 200V - Tubes
Jim:
Adding your AM interests to the equation does change things quite a bit.
Now I understand the need for added headroom.
>From what I've heard, CE exciters put out very good AM in stock form,
provided you have enough linear gain to get the RF level to where the
yAM'ers can hear you.
For what it's worth, I've used my 200V on AM, driving the 3-1000Z to just
under 300 watts of carrier, with excellent results. I used it a few times
to check into an AM swap net on 75M, and surprised the heck out of people
when they found out what I was running. You do have to watch the scope very
carefully to set the levels, but it's a real kick to get good reports.
I'd be interested in hearing from other CE owners that have used their gear
in AM mode. I plan to try a 20A/600L on AM one of these days just to mix it
up a little.
Good luck with your project.
73, George - K1GXT
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jim Candela
Sent: Wednesday, February 18, 2004 1:45 PM
To: [email protected]; 'Radio Central Electronics'
Cc: 'Chuck Ochs'
Subject: RE: [Central-Electronics] CE 200V - Tubes
George,
Thanks for the thoughts and comments. I run a lot of AM (don't shoot
me!) and with AM linear, the maximum RF output is about 1/2 the final amp
plate dissipation, and about 33% carrier efficiency (doubles at 100% sine
wave modulation). I don't have the exact numbers at my fingertips (I am at
work), but I have gotten 16 watts out from my 20a when the finals dump about
17-18 watts each (7591's are rated for 19w plate dissipation). This gives me
about 65 watts pep rf output at 100% modulation. I can do 20 watts (on 80m),
but the trapezoid pattern shows non-linearity from gain compression when the
modulation exceeds 80%.
My point here is that for AM, I need to have 35-40 watts plate
dissipation. A 2E26 is rated for 13.5 watts, so that gives me 27 watts. This
is also a tube designed for class C service, and non linearity when running
in linear mode is something I am unsure about. The 20A driver capability
varies by band, and vintage of the 20a. I have modified the early design so
that I can get about 25 volts peak grid drive from 160-40 meters, whereas
the stock driver could only do a little more than 10 volts peak. The new
stock driver with the modified cathode follower seems to put out like a SOB
on 160m (40v pk), but that drops to about 10 volts on 40-15 meters. This
assumes the VFO is putting out at least 7 volts p-p.
My next move is to take my old driver modification, adapt it to include
the neutralizing circuit, and If I can make it work, THEN change the driver
tube to a 6S4 instead of 1/2 12BH7. The other 1/2 12BH7 (for driving the
6E5) can be replaced with a silicon diode like a 1n4148, and change the 1K
series resistor to about 2.7k. I already did the diode thing on 20A QRO #2,
and it works fine. I need to change driver tube types because I am currently
exceeding the maximum plate dissipation on the 12BH7, and the 6S4 looks very
similar but with a much higher plate dissipation rating.
I'm still hoping to get 60-70 watts pep output from readily available
tubes. A single 6550 (shoe-horned), or a pair of EL34's would do. The EL34
shows the most promise, and this is doable if I can get 25 volts peak grid
drive as described above. The 6550 biased up at -33 volts g1, 270 volts g2,
600 volts plate. I can drive it on 160 m into Ab2 where grid current is
drawn, and it's beautiful. I don't think however that I can make this fly on
a 20a even modified as described above. the EL-34's (mine are Svetlana)
work, but its too early to brag about them. These were never designed as a
RF tube, and the interelectrode capacitances are high, and the lead lengths
to the elements from the socket are not short.
The neutralizing circuit seems to allow for all the capacitance within the
EL-34, but so far I can only drive them correctly on 160 meters. That said I
can tune up on all bands 160-15 meters with no parasitic oscillations.
Without the Neutralizing circuit I tried the EL-34's, and they worked on 160
fine, and oscillated on 80 meters. Removing one tube, and 80m was stable,
but oscillated on 40m. This is encouraging that I have achieved stability
with a non rf tube with lots of capacitance, and lead inductance. I got
lucky.
I'll keep you posted, lots of work to do..
Regards,
Jim Candela
WD5JKO
George Maier <[email protected]> wrote:
Jim & Chuck:
It is nice to get a fun thread going!
I've been following your QRO adventures with interest Jim, and something
occurred to me recently. Mixed in among the CE boxes around here, I have a
Lakeshore Phasemaster II, which has a very strong, almost family resemblance
to the 20A. The main difference is that the Phasemaster has a single 6146
in the final, and claims to be a 75W PEP rig. I can't tell you what it
really does, I've never fired it up. The filter caps are shot, so it's
another project in the waiting.
Anyway, your QRO pursuit, and the 6146 in the Phasemaster kicked off a crazy
thought. It occurred to me that a pair of 2E26's might be something to
consider in the 20A. As you probably know, the 2E26 is 1/2 power version of
the 6146. The C-in, C-out, and C-gp are very close to the 6AG7 on a per tube
basis, but the transconductance is only about 60%, so more drive would be
required. Of course the operating conditions are different, but that's true
in every scenario you've looked at. I'd think you'd get around 80W PEP,
which drives nearly any PA to full o/p. Something to consider !!!
To Chuck's point on the 6L6's in place of 6550's, that's actually an
interesting idea, but I'd be hard pressed to modify my 100V or 200V for the
difference in the price of the tubes. I have heard good reports about
Russian tubes, so maybe that's the way to go, although Ken Grimm raised the
issue of size difference here a while back, i.e. - some tubes are taller. I
think making a new top cover for the PA compartment with extra head room, is
a lot easier than rewiring the PA.
Speaking of that, has everyone heard about Winged C brand ? According to an
AES flyer, they're actually the old Svetlana brand, but Svetlana lost the
rights to use that name the US, so they are now known as Winged C. New
Svetlana tubes being sold in the US are actually Sovtek. Go figure !!!
As for the attenuator between a 100V/200V and a 600L, I used to think it was
silly to heat the room up with wasted power, but now I agree with you.
Originally, I quit using my 600L because the power control on the 200V was
too low to trigger the internal scope. I do have an MM-2, so I could still
see the big picture, but not the whole RF chain. The 600L adds about 5.5 dB
in signal to a barefoot exciter, so it's probably worth it to have 350W of
"no tune" power available.
Vy 73 all around,
George - K1GXT
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jim candela
Sent: Wednesday, February 18, 2004 7:28 AM
To: 'Radio Central Electronics'
Cc: Chuck Ochs; [email protected]
Subject: RE: [Central-Electronics] CE 200V - Tubes
Chuck,
I am enjoying this thread about tubes immensely. You mention going
to a
lower power output tube to better match the low drive needs of the 600L. A
6-10 DB pad is not a bad way to go since no rig mod's are necessary.
I am working on a 20A QRO project (#3) and since adding a
neutralizing
circuit, I can try all sorts of tubes. Last night I shoe - horned a single
6550 into the 20a! Think of the hemi under glass 1964 Plymouth Barracuda. A
tight fit, but it went like a heck. Anyway, I have found only two tubes that
provided wonderful linearity, with high power sensitivity in my 20A projects
(the 6AG7 was not one of them). Those are the 7591, and the 6550. The 7591
(also comes in Novar as 7868, and 9 pin as 6GM5) is in a similar class as
the 6550 with ratings reduced about 50%, and is the same size as a 6V6. It
does however have a different base pinout (sigh), but makes up for that with
two G2 socket connections. There is a 6 meter AM rig using a 7868 to drive a
7984, so the 7591/7868 are good RF tubes with VERY low interelectrode
capacitance. The 6GM5 may be good too, but only one socket connection for
G2. I have never tried the new production 7591-EH (in a bulb the size of a
6L6GC), and the old NOS 7591's are pricey. You can get the 7591's on Ebay as
part of a amplifier sometimes cheaper than the tubes by themselves. Look for
a dirty, and non working Sansui 1000a AM/FM 50 watts RMS / channel tube amp
as they have 4 of them inside (not the Sansui 1000).
I wonder about a simple mod to the 100v where the 6550 Plate B+
comes from
the LV B+ instead of the HV B+. If you try this, make sure the tube is
biased right, and if so, it should work very well at a reduced power output.
Just a thought for you 100v/200v gents to ponder.
Regards,
Jim Candela
WD5JKO
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Chuck
Ochs
Sent: Tuesday, February 17, 2004 7:18 PM
To: [email protected]; 'Radio Central Electronics'
Subject: Re: [Central-Electronics] CE 200V - Tubes
Hello George--
Gross generalizations here, but the Russian tubes are vastly superior to the
Chinese variety. I expect that in a few years, the opposite will be true, as
the Chinese clean up their quality control problems.
You are right to mention that using a 100-V or 200-V with 6550s is serious
overkill, when driving the 600-L.
I haven't had a chance to experiment yet, but the idea of going to a less
powerful (and less expensive) tube, such as the 6L6 / 5881, or even the 6V6,
has occured to me. This may result in identical overall operation with
vastly lower tube cost. Has anyone on the list tried this? I have
successfully employed this technique with audio power amplifiers.
Chuck N1LNH
----- Original Message -----
From: "George Maier"
To: "'Radio Central Electronics'"
Sent: Tuesday, February 17, 2004 9:47 AM
Subject: RE: [Central-Electronics] CE 200V - Tubes
> Thanks Chuck - your advice is both sage and sensible, and I'm sure that we
> all agree that Tung-Sol is the best.
>
> I guess my question deals more with how the others (Sovtek, Svetlana,
Valve
> Art, Winged C, etc) actually perform, and what is different about them.
>
> If the RF o/p is not as high, but the linearity is the same, some people
> might not care. For example, when driving a 600L, a 100V/200V is total
> overkill, and the exciter power control is at or close to minimum anyway.
> Also, if you run barefoot and get 80W instead of 100W, that's less than
1.0
> dB, and no one would ever notice. In my case, I typically drive a
3-1000Z,
> which takes most of what the 200V can put out, but there's still some room
> to spare.
>
> If on the other hand, the other-than-Tung-Sol tubes do not exhibit good
> linearity, or don't last very long, that's quite another matter.
>
> Any comments (from anyone) will be appreciated.
>
> 73, George - K1GXT
>
>
>
>
>
> -----Original Message-----
> From: Chuck Ochs [mailto:[email protected]]
> Sent: Tuesday, February 17, 2004 1:49 AM
> To: [email protected]; 'Bill Marx'; 'Radio Central Electronics'
> Subject: Re: [Central-Electronics] CE 200V
>
> 6550 tubes--
> The best ones ever made were the Tung-Sol variety. Highly sought after for
> audio amplifiers also. The currently available types pale in comparison.
> Chuck N1LNH
> ----- Original Message -----
> From: "George Maier"
> To: "'Bill Marx'" ; "'Radio Central Electronics'"
>
> Sent: Monday, February 16, 2004 9:04 PM
> Subject: RE: [Central-Electronics] CE 200V
>
>
> > Looks like mine did when I first got it.
> > Speaking of the "V", has anyone on the list taken the time to evaluate
the
> > various types of 6550's that are around these days? Prices are all over
> the
> > place, but I've been wondering what's good and what's not.
> > Thanks & best to all,
> > George - K1GXT
> > *** CE is all you need - period !!! ***
> >
> >
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]] On Behalf Of Bill
Marx
> > Sent: Monday, February 16, 2004 5:31 PM
> > To: Radio Central Electronics
> > Subject: [Central-Electronics] CE 200V
> >
> > This list has been quiet of late. Here is a 200V to get everyone
excited.
> >
>
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4675&item=3078714415
> >
> > -Bill W2CQ
> > _______________________________________________
> > Central-Electronics mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/central-electronics
> >
> >
> > _______________________________________________
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> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/central-electronics
>
>
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