Viking 2 Hammond interstage transformers

[KA9EGW]

So I now have both a 124A and a 156...and they both look awful puny for the job at hand [replacing the stock audio driver transformer]...which is better?  Core sizes look the same...do I go with the one with the heavier wires?

[w7fox]

The 156 is a choke.  If you mean 126, it is a 1:1 ratio.  The 124A is 1:3 ratio.  The 126 would be suited to class AB2 or B, while 124A would be suited to AB1 (no grid current).  I think the Viking is AB2, so the 126 would be the one to use. 

[KA9EGW]

Hmm...check this pic out...or would I be better off going with the 6C4 hot cathode splitter?  Just TOO dang many choices on this one...according to AES the P-T156 is equivalent to thee Stancor A53C...confused, I am indeed...

[N2DTS]

The stock Viking 2 is ab2, is it not?
If so, it takes grid current and power to drive, so a phase splitter will not work.

The handbooks (Bill Orr) have info about picking a good driver transformer in them.

The DX100 used a postage stamp size driver transformer, as did the Gonset G76, the 32v series rigs had a large driver transformer.

I would think you would want a low impedance source to drive grids that take power, 1 to 1 or a step down?
Really low plate resistance triodes were popular as drivers, like the 6B4.

[KA9EGW]

There is some controversy about whether the 807's ever need to be driven into AB2. 
These are both 3:1 step-downs, and have received positive reviews right here on this board...then too so has the phase splitter idea...I was just struck when I took them out of the box how tiny they looked...I guess I was expecting something bigger...

[WQ9E]

I have used the P-T156 from AES to replace the failed Stancor A53C unit in many rigs and it works fine.  The original Stancor unit was used in numerous Johnson and Heathkit rigs and it fails because of corrosion of the very fine wires due to the acidic paper.  The little "modulation" transformers used in Central Electronics phasing SSB rigs have the same corrosion/failure issue.  I think I first used one of the AES transformers to replace the failed unit in a Valiant I restored back in 1995 and it is still working fine.

[KA9EGW]

I was under the impression the stock transformer had core saturation issues...if that's not th case ten away we go...after I get 3 other projects out of the way first that is...

[W3GMS]

The first thing you need to do is to determine what class of operation you want to run or need to for the modulator.
Once you answer that question your simplest options will be:   

1) If AB1 you can use a hot cathode phase inverter or similar topology.   You can also use a driver transformer. 

2) If AB2 operation is needed then you need a scheme that will support the grid current demands.   You could use a direct coupled schemes that has the capability to support grid current or a use a driver transformer with the required turns ratio so it can deliver the grid current when demanded. 

What are your design goals for this transmitter?   Do you want it to sound like a BC rig or do you want to have it deliver some low distortion communication quality audio?  If its the later, then the transformer is likely your simplest approach if indeed the tubes need to be biased for AB2 operation.   In such cases I have used Hammond transformers with very good results. 

Joe, W3GMS     

[Steve W8TOW]

the Hammond interstage transformer to use is the PT-123-E (20A14)

This transformer is a split primary & secondary.

I'll post the wiring diagram later today, but I've used this as
a driver transformer in many Vik I, II, Val, Ranger & even my Johnson 500.
(plus many other rigs)

For this application, I assign the side with : Black, Green, Black-Yellow, and Green-Yellow
as the primary. Tie Green and Black-Yellow together. Black is the top, Grn-Yel bottom.

Secondary is Brown (top) Blue (bottom) Red CT
Across the secondary put a 18K 1 watt.
And (also) Across the secondary put a series RC circuit of a .001 uF cap and 1.8K resistor

Again, I'll put the drawing up later as a PDF...
73
Steve 8TOW

[KZ5A]

There is a Hammond 124B that may be the best Hammond choice, same as the 124A but has a high nickle core that is alleged to provide better performance.   That is what I used in my B&W 5100.

On the VK2 my opinion is that AB2 just should be avoided as there is no practical way to go there without incurring a substantial increase in distortion.

73 Jack KZ5A

[Detroit47]

The PT-156 is a drop in replacement and works fine. I have used in stock vikings. I have also used it with a 6c4 as the driver. Great lil transformer cheap too.

John

[W8ACR]

I have two spare original Viking driver transformers. They are yours free if you will use them and if'n you want 'em. I think they are still good, but I guess I don't know for sure.

Ron W8ACR

[KA9EGW]

I appreciate the offer, but that'd leave me with FOUR transformers total, and still just one VK2 to restore...

[WQ9E]

I appreciate the offer, but that'd leave me with FOUR transformers total, and still just one VK2 to restore...

Well there is a simple solution to that.  Just acquire a Viking 1, Valiant, Valiant II, DX-100, etc. to go with your Viking II and then you can use those extra transformers  Winter is far from over so you don't want to run out of projects.

While you are in there make sure to check the 5R4 rectifier tube bases and sockets and clean any dust and check closely for the development of carbon tracks.  The 5R4 tubes and sockets are prone to this issue and I have had to replace a couple of 5R4 sockets because of this problem. 

[KA9EGW]

Sure...the XYL will love that one...she hasn't squawked at the shop growing by 2 KWS-1's, a 75A-4, an HRO-50, a Viking, a Warrior, a 51J variant, an SX115, the Drake 'fraternal twins', a 2nd R-390A, a 2nd KW Matchbox, the "SB-211" debacle, 30 feet of antenna tower, a pallet of shipping boxes, parts for the 813's final project, a spray booth for Junior's airbrush, and 6 friends' motorcycles, plus whatever I'm forgetting that also arrived in the last 90 days...on 'her side' of the fence, so to speak, add in the 3 'foster fail' kittens [who we were just supposed to be fostering but who grew on us], the already-resident cats and the dogs

[WQ9E]

As long as the radios multiply faster than the cats all is OK!  Along with the many radios here we have some house cats, a few barn cats and a barn opossum that thinks it is part of the barn cat family.  Fortunately our German Shepherd Cheyenne (now almost 6 months old) likes cats so the kingdom is peaceful.  She can look pretty ferocious as in this recent photo of her running through the snow but she plays nicely with the other 4 legged creatures although I do keep her away from the "fake barn cat".

 

[KA9EGW]

Oh My God that is one gorgeous Shepherd!   You gonna bring her with when we meet?

[WQ9E]

Cheyenne travels pretty well so maybe she will get to make the trip northward.  Hopefully the weather improves sometime later this month so travel will be better for both of us!  The forecast is for additional snow almost every day this week and it may be very heavy on Tuesday.  It looks like I am going to be spending a lot of time on the tractor clearing our driveway.

I wasn't particularly looking for an all black German Shepherd but I put a deposit down for pick of the litter and Cheyenne was the only pup born to her first time mother.  She has a tiny little white spot on her chest (maybe 9 hairs total) but is otherwise solid black.  Fortunately she is well behaved because at night she can easily disappear when she goes outside.  She and my daughter just headed out into the newly fallen snow.

[Detroit47]

I just put the finishing touched on my Viking 11 last night. It looks real good for being original paint. I recapped and resistor-ed it and did the 12AX7 / 6C4 audio mod. I am getting good audio reports now I am going after my NC303 to mate it with. Just for info I used the  PT-156 driver transformer it works great.

John N8QPC

[KA9EGW]

6c5???  There's one mod uses a 12ax7 and a 6c4, is that the one?

[Detroit47]

6c5???  There's one mod uses a 12ax7 and a 6c4, is that the one?

TYPO 6C4 a thousand pardons

[Steve - K4HX]

Glad to hear it worked out. Congratulations John.

[Detroit47]

Thanks Steve I seem to have more time for my projects since I quit doing repairs for other people.
  73 John N8QPC