How do you match them up...even if they are good ?? ? ?2 tubes are bad enough....and 3 of em is a pita.?

I ran into this same problem eons ago on hb amps.? 2 x really good tubes...when tested one at a time...... but when used in pairs, the current does not split 50-50.? Some were 60-40, and some were 65-35.? ?I have pairs of 4-400A/B/C's? and the pairs of 4-400A's and also? the pair 4-400B's? match up good, with a 50-50 split.? However the pair of 4-400C's don't match up, even though when tested one at a time, put out rated power.?

After that, it was just a single tube for any hb amp.? Need more PO, use the next bigger tube that is available.? ?IE: 3x3, 3x6, 3x10, 3x20.? ?Or 4x5, 4x10, 4x15.? ?Pick just one of either triode or tetrode.?

Nobody puts more than one engine in a pickup truck.? Get a bigger engine.?

On 2/21/2024 7:42 PM, Jim VE7RF wrote:

Why did u have to go through digikey..and not directly with hammond /
dahl ?

I tried ordering my replacment 2K4A XFMR from Dahl/Hammond, and they
told me I had to order it through DigiKey because DK was now their
distributor; so I did. Initially, there was some confusion; the DK
person on email (I cannot hear on a phone, so have to use either text or
email) didn't think there was such a model as what I wanted. I asked her
to check with Dahl/Hammond, who had told me to order from DK; I gave her
the name of the person I'd corresponded with at Dahl/Hammond. She did,
then I got an order-confirming e-mail after a few days asking for my DK
account schtuff. Once I gave that, it was another few days until I got
an ack from DK they had received that info. THEN I waited TWO WEEKS with
no ack they had accepted my order; so I emailed again, they said they'd
check... and finally, a couple days later, I received an e-mail
acknowledging my complete order... and listing a delivery time some
FOUR-PLUS months down the road. I initially emailed Dahl/Hammond in late
January, DK finally sent this email around the middle of March. The
delivery was scheduled, by FEDEX Fright, for the middle of July, IIRC.
As it happened, this all occurred just prior to, and then during, the
first few months of CV-19.

I was finally alerted by FEDEX around the end of June that my XFMR would
be available for pickup locally in a couple weeks, then in a week got
another e-mail it would be on time when they said.

After FEDEX emailed me that last time, they emailed me again several
times, trying to claim my XFMR had been sitting there waiting for me for
a week, and they would return it as "Unclaimed"... as it happened, on
the SAME date they had originally said it would be available for pickup.
I had to have my brother get on the phone with them and he finally got
through to them I was WAITING for the delivery date.

... And then finally, I drove there (turned out to be just a couple
miles away from where I lived at the time), the forklift brought it out,
and I had to cut it loose from the pallet and get it out of the wooden
box, both of which may have weighed almost as much as the XFMR. The
parking lot had a lot of pallets that customers had cut their goods
loose from.

It all was an adventure I don't want to repeat.

Steve, K0XP

Why did u have to go through digikey..and not directly with hammond / dahl ?? ??

NO hv sag at all, that's superb.?

IMO, whatever the B+ is? with amp keyed, and sucking normal idle current is the real no load B+.? ?It has to idle 1st, before you ac apply drive.? ?I really could care less what it is in RX.? ?But that has it's limitations.? Like if EBS is used, etc.?

Alpha? 91 / 99? xfmr's are failing? ?at a high rate these days.? ?Same deal with the older ACOM amplifiers.? The issue is, they have a total of 5 windings on the secondary side..... and in all the failed units, the high voltage winding, is arcing to a lower voltage winding.? ?The insulation has broken down over the years.?

Dahl never went cheap with the insulation..and neither did Hammond.? I still have hammond plate xfmrs made in the late 50's that still function, even with floating CT's....and also stuffing 247 vac into the 210 vac pri.?

Some oil caps were meant for energy discharge, ( like laser discharge)? and have higher internal ESR.? ?They will work for B+ applications, but have to be-derated for voltage.? ?Typ oil caps used for B+ applications, used in TX / PA applications have zero esr.? ?I can measure ESR on my B+K 875B, since it measures AC resistance, instead of DC resistance.... but only at 1 khz.? ?It uses a 1 khz square wave, so it can't be used on the pri of a plate xfmr, to measure resistance. On stuff like 450 vdc lytics, the measured esr at 1 khz, will be a lot lower vs the normal 100/120 hz.? Better LCR meter's will measure at several freqs.? I have to factor in a? correction factor.? ?EG: my big 10,000 uf @ 450 vdc lytics (3" diam x 8.625" tall, 3.3 lbs) measure just .005 ohms at 1 khz..... when in actuality, they are really .0159 ohms? @ 120 hz.??

?

Are you still going to use the choke....or just add the 38 uf filter cap onto the output of the existing B+ supply ?? ?Either way, I would insulate the oil cap from the chassis.?

?

So far, when comparing PSUD-2? ?vs? reality.... it's dead on for the most part, provided every last thing is entered correctly.?

I talked with Duncan, who designed it.? I have been using it for yrs now.? The previous versions had a lot of short comings, so I developed some work arounds.?

Just before CV-19,? I mentioned a bunch of issues with the current PSUD-2? ?with Duncan.? ?A lot of it was software limitations.? Like when you add an LC section, with just a series choke, and then use the bypass cap at the cold end of the plate choke for the ...'C'.? ? It results in a ton of...'noise'.? The giveaway is when it? runs at a crawl.?

Duncan has my mile long list for the new? PSUD-3.? But CV-19 came about, and it all went to hell.?

PSUD-2? won't handle? negative power supplies, only positive supplies.? ?It won't handle glitch resistor's,? nor? 3 phase power,? nor resonant chokes.? It won't spit out results for ripple, other than 100/120 hz.? ? ?It's pretty good for what it does though...and is easy to use.?

Hi Jim,

I've spent more time modelling it now but I'm still not happy with the overshoot with sudden load changes

Plus, I've come by an "energy storage" capacitor rated 38uF at 8kV. (It's 22" tall, 6" x 10" !)

I'm not sure what parameters of a capacitor warrant the "energy storage" labelling... don't they all do that?... but it appears to be polyester film or PIO in a big metal can. Maybe originally intended for PFC applications. What's not to like?

PSUD indicates it will fix my ripple voltage problem.

Thanks for your awesome info on using chokes.

Tim

You are correct.? A MOV? from each winding...to chassis? is a wasted effort.? ?I didn't think of what happens if the spark gap arced, when the choke is part of a choke input (resonant or not).? With the choke temp shorted, via the spark gap... (or choke effectively shorted via 2 x MOV's), the B+ would skyrocket...and fry the lytics in the supply.? ?Those 16 uf? @ 7.5 kv oil caps in henry amps (they still sell em)? were notorious for arcing? to the the steel casing, when used on 6+ KV? HB B+ supplies back in the 70's and 80's.? I used 4 x 47 uf @ 4.5 kv oil caps in series-parallel...on a 6800 vdc supply. One day, the line V drifted to the high side at 247.3 vac..... and the B+ rose to 7 kv.? ?The 7 kv arced sideways, just under the insulator on the oil cap, to the side of the hole, where the threaded rod protrudes through the hole.? It blew out the red washer that sits between the steel casing....and the bottom of the? glazed ceramic insulator.? ?My? 'fix' was to use a 1/4" thick huge sheet of that red micarta (HV fiberglass)? under all 4 x oil caps...then 1/8" thick? sheets of micarta between each oil cap.? Problem permanently solved.? Oil caps insulated from each other...and the chassis.? ?

Yes, I'm a strong advocate of insulating any choke from the chassis.? ?With the choke insulated from the chassis, there is no V potential? between the choke terminals / winding....and the steel frame.? ? To arc from the windings to the chassis, it would 1st have to arc from windings to the frame...then? from frame to the chassis...and that's not gonna happen.? Think of it as a contactor, it's just then 2 x gaps in series, and you have to arc both gaps simultaneously.? ?The windings have B+ on em...and the chassis is grnded.? The choke's steel frame is between em...and floating.? ? I can't draw any leakage current at all ( windings to chassis)? with my hi-pot tester, even after 2 hrs.....but it only goes up to 15 kvdc.? ?I also tried hi-pot testing from windings to frame, then? frame to chassis...and still can't pull any leakage current with 15 kvdc.?

?

On a C-L-C setup, even with the choke shorted out via a vac relay, B+ value stays the same.? ?I put both the adjustable spark gap and also? the Kilovac SPST-NC ceramic vac relay across the choke terminals. The vac relay is there, so I can compare the calculated ripple, with and without the choke.? ?With the choke shunted, it becomes one big C filter...with C1 and C2 now directly in parallel.? ?I had bought a bunch of nib spst-nc kilovac relays yrs ago...cheap.? They have 12 vdc coils.? Nobody wanted em, since they are just spst...and also NC.? ( choke shunted with vac relay coil? de-energized).? ?The relay is there for an experiment...so I can do rapid A/B testing.??

On 2/20/2024 9:42 AM, Jim VE7RF wrote:

I was thinking about a RVS connected diode across the choke..... but
Hammond/dahl read me the riot act, said...'don't even think about
it'.? ?They are correct of course, since the normal Voltage across the
choke will swing up/down a bit like +70 to +100 vdc...then swing
negative the same amount.? The diode would conduct on 1/2
cycles....and short out the choke.

A MOV may well work, BUT if it fails, it will fail shorted every
time.? ?MOV's really should be fused...but that would require a proper
sized HV fuse.? Modeling in software, the peak V can easily be through
the stratosphere, when excess amounts of fault current are drawn
through a choke, like almost triple the B+ in some cases.

Well then... since what we're REALLY concerned about is keeping the
voltage difference between the choke winding and iron core low enough
that it never arcs over and causes damage, what about a high-voltage MOV
(couple hundred volts or so, fused, as you suggest) between either choke
terminal and the choke frame?? Perhaps the real answer is to both
isolate the choke body from the chassis as you've done, and use the MOVs
to reduce the possibility of arcover damage? (plus use the spark gap!)
The two MOVs are effectively in series across the choke; so if they're
HV like 180 - 200V or so, then they will clip at 360 - 400 volts or so,
which is not far from what your 0.005" spark gap should arc over at.

Then again, I suppose since we isolate the choke body from the chassis
on insulators, we really don't care if it arcs between the winding and
frame. Or do we...

The reason I'm going on about this is because although I've got the new
XFMR to put in my 2K4A (haven't put it in yet), I never thought before
about the possibility of the choke having also failed. So now, when I
finally do install the XFMR, I'll also remount the choke on insulators,
as you've done (plus the spark gap).

Then again.... if those MOVs, or the spark gap, ever fire, then they are
effectively shorting out the choke... and so our B+ tries to shoot sky
high; and if it does for longer than a split second, we have Sh|7 City
inside the power supply cabinet as the electrolytics (IIRC, mine has
electrolytics instead of an oil cap for C1) blow the heck up... ===8-O

The spark gap is dead simple.? And yes, probably? ? .005" is ample.?
?Actually, .032" is good for 1100 V..so that amounts to 1100/32 =? 34
volts per .001".? ?.005" = 172 volts.? ?I believe mine is aprx .005"
The thickness of a 8.5" x 11" sheet of printer paper is typ .005"
thick. (.13mm)

Through the years, I've gotten pretty good as estimating 0.032" gaps,
since I've gapped spark plugs since I was smaller than a wee lad? 8-)

Steve, K0XP

I was thinking about a RVS connected diode across the choke..... but Hammond/dahl read me the riot act, said...'don't even think about it'.? ?They are correct of course, since the normal Voltage across the choke will swing up/down a bit like +70 to +100 vdc...then swing negative the same amount.? The diode would conduct on 1/2 cycles....and short out the choke.?

A MOV may well work, BUT if it fails, it will fail shorted every time.? ?MOV's really should be fused...but that would require a proper sized HV fuse.? Modeling in software, the peak V can easily be through the stratosphere, when excess amounts of fault current are drawn through a choke, like almost triple the B+ in some cases.

The spark gap is dead simple.? And yes, probably? ? .005" is ample.? ?Actually, .032" is good for 1100 V..so that amounts to 1100/32 =? 34 volts per .001".? ?.005" = 172 volts.? ?I believe mine is aprx .005"?
The thickness of a 8.5" x 11" sheet of printer paper is typ .005" thick. (.13mm)

?

On PSUD-2,? I don't use the resistive load, I use the constant current load.? ? And? then also have the option to toggle between any 2 x distinct current loads, like? say 200 ma, then 800 ma... OR the other way around, like 800 ma, then down to 200 ma.? ?It won't simulate? ssb,? ( but sorta).? ?When u toggle between 2 x different loads, it's like? right now, asap, instantaneous.? ?On CW, you have a 5 msec rise and decay time.? On PSUD, it's 0 msecs.?

?

PSUD-2 will not handle a resonant choke.? ?The problem with the resonant choke, like used in Henry amps is.... the B+ is only .9 X sec AC voltage.? ?With a C input filter, it's 1.414? x sec AC voltage.? ?IE: 6000 vac sec on a 8K ultra = 5400 vdc no load.? ?You coulda got the same 5400 vdc, by using? a FWB + just a (5400/1.414)? =3819 vac sec AC winding.? ?If a FWD was used, the sec is then just 1909 vdc.? ?The resonant choke setup also requires a huge amount of bleeder power at all times.? ?The 8k ultra uses? 5 x 20K @ 100 watt wire wounds in series.? ?That mess sucks 300 watts? CCS, or 60 watts per resistor...and all 5 of em run stupid hot.? If just any one of em opens up, the B+ soars to? 6000 x 1,414 = 8484 vdc.?

With the bigger choke values, like your 10H, they require a? smaller resonating cap...which is good,? BUT the 10H choke has a lot more dc resistance vs a 1-2-4 H choke.? ?All that wire has to fit the core, so they have to use smaller ga wire = less current handling capability.? ? The issue with the resonating cap, like when a 4 H choke is used is.... the choke + cap form a 120 hz notch filter.... fine, BUT all the harmonics of 120 hz will? sail right through the resonating cap.??

On a 10H choke, it requires a .1759 uf resonating cap.? ?A 4H choke requires just .4398 uf.? ?(20 hz will sail right through a 2 uf cap).? 240 hz will sail right through a .1666 uf cap.? It just gets worse with the higher harmonics of 120 hz...like 240-360-480 hz etc.? ?Then u have the issue with now 2 x dc currents flowing through the choke, the main current, and also the circulating current in the choke.? The smaller the choke value, the higher the circulating current.? It's bad enough with a 8 H choke, but with a 4H choke, the circulating current is as high, or higher than the main current.?

To kill the harmonics, ideally the C1 cap needs to be a decent value.

John Lyles, K5PRO, when he worked for Broadcast engineering, designing single phase 5 kw? FM broadcast PA's, told us that the FM pa's had to meet this spec, called an ...."AM noise spec" .? The supply used a resonant choke.? (resonating caps were a series pair of .9 uf oil caps, like used in microwave ovens).? Caps were sent to the choke manufacturer, and the choke was hand wound, so it resonated around the supplied caps, .45 uf for the series pair).? In some cases the choke is made to a larger value, so it can be used on 50 hz.... then tapped down to a lower value for 60 hz..so resonating cap pair stayed constant.?

?

Problem was, the resonant choke would not meet the....."AM noise spec'.? (I forget how big the C1 oil cap was, think it was like 16uf to 20 uf).? ?His fix was to wire a LC filter onto the end of the existing resonant choke + C1 cap.? This time the added LC filter does? NOT have it's choke resonated.? It's there to kill the harmonics of 100/120 hz.? IE: it ends up being a (resonant) L - C1? - L2 - C2? setup.?

?

A simpler? ?C-L-C woulda done the same thing, and also coulda used a much lower secondary Vac.??

I also wanted to try yet another config... using the same? C-L-C? setup, BUT resonating the choke.? Got a buddy in W5 land to simulate it on LT SPICE for me.? It results in a lousy 4 db improvement at 120 hz.? The main drawback was, the existing, superb harmonic attenuation? was ruined by the resonating cap.? Same deal, harmonics sail through the resonating cap....and attenuated only by whatever value my C2 cap is.?

The consensus was to not mess with a resonating cap on a C-L-C config.?

As far as testing your choke for heat, like with your proposed? 2.0 to 2.5 amp? CCS load,? that's? easily tested by using a small lab supply, with current limiting, like a 0-160 vdc @ 5 amp variety.?

With 850 ma into 28 ohms =? 20.23? watts.? ?2.0 amps into 28 ohms =? 112 watts.? ?2.5 amps into 28 ohms =? 175 watts.? When more than rated current is drawn the dc resistance increases, then it slowly goes into thermal runaway.?

?

But for FT-8 use, like (I think)? 15 secs on, and 15 secs off, duty cycle is 50%, so may well get away with it.?

?

Another option is to use a lot more C....since ripple is inversely proportional to uf.? Doubling the uf results in a 6db? reduction in ripple.? ?But you would need one helluva lot of uf.?

Another option is a smaller choke, like 1-2-4 H, but with a lot higher current rating.?

Mine is rated for 3 amps? CCS, and is 4 H....and good for ( I think) 15 kv..... but it's big, 127 lbs.? Stone cold with 3 amps? CCS.? With 6 amps CCS, it runs pretty hot, (195 F)? right where the gapped cores reside.?

On Tue, Feb 20, 2024 at 04:19 PM, Jay Sturtevant, K2ZT wrote:

What is W8JI's email address for ordering parts?

?

Thanks.

?

Jay, K2ZT?

Here.? ? ?https://www.ctrengineeringinc.com/contacting-us-please-read/

DigiKey delivered my Alph 99 transformer exactly 7 weeks after ordering it for a fairly reasonable price. The new one says "Peter W. Dahl" on it and it is STOUT!. NO Hv sag at full output.

Good on ya, DigiKey!!

73

I notice in the circuit of the Henry 3K, 4K EHT supply there is a 10H choke, with a 0.2uF capacitor *in parallel*.

0.2uF // 10H makes a parallel resonant circuit at 120Hz, nice trick to up the impedance and improve ripple rejection.

Can't model it in PSUD so I'm just trying LtSpice....

On 2/19/2024 7:52 AM, Tim Fern wrote:

I will definitely insulate the choke frame from the chassis, I think
your analysis of Henry Amp choke fails is spot-on. And I’ll copy the
Acorn-nuts spark-gap across the choke. What width gap did you choose?

I wonder if a VERY careful examination of both the choke and the chassis
and choke mounting hardware, including at the mounting holes for screws,
might find some sign of soot from such HV arcing?? The soot resulting
from when my 2K4A HV transformer winding arced to its frame right
outside the winding wasn't initially visible, until I happened to wipe
my finger across that area and saw the soot on my finger. Finding such
soot might help prove this theory of the choke arcing to the chassis.

Also, I, too, was wondering what spark gap Jim uses across the choke?
I'd think you'd want it as small as possible; i.e., 0.005" if possible,
just wide enough that dust across the acorn nuts doesn't short out the gap.

Finally... I'm wondering whether a high current MOV might perform the
function of the spark gap, except more reliably?? After all, we use them
on the filament pins, where they're taking the full current of a
discharging HV capacitor through the tube. It seems to me that I've seen
MOVs connected across chokes in the past.

Steve, K0XP

I recently acquired a few Alpha amplifiers that needed repair.? Along the way I decided to test all 10 tubes I had on hand.?

I put each 3cx400A7 in one at a time, let the filament run for a while to burn in. I Applied 1500 volts for 10 minutes or so.. then Keyed up While monitoring Grid and Plate current for 5 minutes.

I noted idle current and then applied 15w RTTY drive on 20 meters and noted output power.?

Out of the 10, Two where bad, one had open filament and the other a grid short.? The other eight where all good.

Output power for those eight tubes:

175 w
175 w
175 w
150 w
140 w
120 W
100 w
75 w

I let them run each tube keyed for 5 minutes or so and power was stable, and no tuning would produce more.? All tubes ended up at pretty much exactly the same tune and load.

ONE of the new tubes made 50W but after a cycle of key OFF and Key ON power rose up. 75, then 100, then 120.? It ended up at 175 over about a 10 to 15 minute period.? Interesting to see it rise up like that.? Something was coming back to life.

ALL other tubes made power instantly.

What is interesting is that even the tubes that have lower output power and gain at 15w, make FULL power in the amplifier.? ?I can take the two weak tubes, 75 and 100, and put them in the amp and make 1500w out with a woodpecker.??

I can put the best three in the other map and make 1800w.? ?I can remove them and put the weakest three in the amp and make 1800w.

Is there a better way to test power tubes?? Or do you really need to just test them to full output?? I had reservations about applying 2700 volts to them right away, that's why I used 1500v and low drive. Some of the tubes where new and marked 1980 so some run time is probably advisable at low voltage.

I guess the drive and or added B plus is overcoming the loss of gain?

C

Thanks Jim, loads of great info here, just what I needed.

?

Your Dahl choke is a beast, wow, I thought mine was a monster, but life has taught me that somewhere, there will always be a man with a bigger one :-)

?

It might use my choke on a big single-phase triode supply here. I like the sound of -129dB ripple filtering…. One of the problems using *any* tube amp with FT8 is that your radio neighbours report the signal is wide….. because they see the 100Hz sidebands on their decode screens even when they’re -40, -60 or -80dBc ….ask me how I know this :-(

?

PSUD is new to me...what a great tool, I’m playing around with it now. I can change the load R to simulate what happens with different plate currents as power is applied….. but were you able to simulate how the output voltage changes with sudden changes in load R? I can’t see how to do it in PSUD?

?

I will definitely insulate the choke frame from the chassis, I think your analysis of Henry Amp choke fails is spot-on. And I’ll copy the Acorn-nuts spark-gap across the choke. What width gap did you choose?

?

The DC resistance of my 10H choke is 28 ohms, I currently have a big 56 ohm glitch resistor, I might swap that for a similar 33 ohm one here, depending what C2 I end up with. I know how much energy the tube can take.

?

The 0.85A CCS rating is a bit lower than I would like. I’m wondering what would happen to it at 2A or 2.5A? Does it just risk over-heating? or might the core saturate too and stop it being an inductor? (Am pretty sure it’s not a gapped “swinging inductor”.)

?

Best regards

?

Tim

开云体育

Actually, I applied for membership to that group a few weeks ago, but still haven't heard from a moderator either way. Have been trying to read through the "back issues" of posts in the Archive, but something seems to be resetting when I try to read messages going forward in time, and instead the next message displayed is the prior one. Probly my phat phingerzes hitting the wrong key? 8-)

73,

Steve K0XP

There is an Alpha group here on "Groups.io", rather specific to the 9500, but I've seen inquiries regarding other Alpha models. In addition, Glenn Pladsen (AE0Q) often posts replies to issues posted there, and sometimes will email you direct regarding things posted on the forum.

The Alpha 9500 group is HERE: /g/Alpha9500

Good luck.
--
73,

~Alan

Hi,

I am? looking for Bandswitch Rear Wafer? E4C-N18 for my Alpha 78.

Anybody in the group either has one for sale or know where to buy it?

Thanks
73 de Arturo, LU6ETB

开云体育

Dr Alex is alive and well. I bought and paid for some doorknob capacitors just yesterday.

I try not to shop anywhere else.

73, Alek VK6APK.

On Sun, Feb 18, 2024 at 09:25 PM, Peter Voelpel wrote:

There are? Russian 4?H roller inductors..

They are available at Dr. Alex, UR4LL:

?

?

73

Peter, DJ7WW

I saw those 4 uh? roller coils. I didn't get an answer back from Dr? Alex as to? what ga wire was used, or condition of them.? I have never ordered anything from him...so have no clue what the shipping costs are to VE7.? ?At the time, the war had just started, and Dr Alex? had vanished, and had to temp relocate for his own safety.? He showed back up several months later.? They look like a viable option, albeit shaft diam is < 1/4" (6.35mm),? non issue, as an adaptor can easily be fabricated by drilling out a 3/16" coupler? to? (I think)? ?the Russian 5mm shaft.?

?