Viking II Interstage Audio Xfmr???

[WBear2GCR]

Probably well known to "those skilled in the art"...

In yet another nefarious plot to foil my efforts, the recent aquisition of a venerable Viking II is just another episode in the master plan to absolutely keep me off the air with anything resembling a decent power level or signal quality. No matter which path I start in, the roadblocks and deep sinkholes appear suddenly without explanation. True. Sad but true.   

Ok, so skipping the part about the low voltage power supply iron emitting the magic blue smoke, and my getting a parts chassis in trade for a fine bit of TMC stuff, thus seemingly saving the day? Yeah, let's skip that part.

So, I decide that TODAY IS THE DAY to go through the rig, replace the smoked power transformer, replace ALL the icky old caps and make a magical and quite theatrical reappearance on 3885 with a marvelous plate modulated boatanchor signal. Well, about 3-4 hours into the cap swap, transformer transplant and the "wtf is this doing here?" part of the process, I'm down to the brass tacks of it and the finish line is close - maybe another 3-4 hours off into the evening. BUT TODAY.

No way. The ohm-eater says that the primary of the interstage driver transformer is as open as the St. Lawrence Seaway is in the summer. That's open. NG. Dead. Defunct. Gone. Not gonna do it.

Ergo, this post. With story to boost the empathetic response.

Anyone know the specs of the thing?? In particular the turns ratio or better still the impedance ratio? I'll settle for the DCR measurements if that's all I can get and surmise the rest from the circuit if I need to.

How about a good cheap fast source for a replacement?
Your junquebox?

Won't you please HELP this poor hapless ham?

Seriously, any good ideas or actual help is appreciated.

           _-_-WBear2GCR



PS. of course the interstage tranny is MIA from the parts chassis, of course.

PPS. yes, yes, I can design, install and use a circuit mod that will absolutely work great and NOT USE a stupid interstage transformer at all - but then we're into drilling and blasting and all of a sudden it's a bigger, larger, more complicated and royal PIA project that isn't just putting an old Viking II on the air... KISS was the idea.

[W1GFH]

The Hammond 124/ PT 156 is the one I've seen used as a replacement.

http://www.hammondmfg.com/124.htm

And Google is your friend:

http://members.cox.net/n4jk/viking_ii_.htm

[WBear2GCR]

Thanks, good info.

Think maybe I have a local source for the Hammond unit.
Maybe.

         _-_-bear

[K1MVP]

The Pt-156 driver transformer is/ or was available from Antique Electronic Supply in Phoenix Arizona
for about 10 to 12 bucks, if you are looking for a "generic" type driver transformer.
                                                  73, K1MVP

P.S., I think you can order online at www.tubesandmore.com if I recall correctly.
P.P.S., I just checked,--the price and it has gone up to $16.50,--been a while since I bought one.   

[The Slab Bacon]

Bear,
         Hammond 124D interstage from antique electronic supply works just fine. I have used these in V-2s, valliants, rangers, and apaches. They are relatively cheap and have enuff tapz to configure to your needz.

If you dont plan any really heavy modz to the modderz, and still plan to run them AB1 with no grid current, just about any 3:1 step up interstage will work just fine. If you got something close in the junk box, give it a try, it will prolly work.

And.......er.....furthermore....... If you are planning some descent audio out of the V-2, bulldoze the whole audio section out and do the 12AX7 / 6C4 thing!!

                                                                   The Slab Bacon

[W1GFH]

Yeah but be sure to use a Bugle Boy 12AX7...

[Bacon, WA3WDR]

Has anybody tried a 1:1 transformer here?  It seems as though a lot of designers went with 1:3 primary to secondary ratios, but in the Viking II it looks to me like a 1:1 would work OK.  I took the 807s out of my Viking II and put in 8417s with cathode follower drivers and no driver transformer, so I don't know.

Allied Interstage Audio Transformer
Pri 10K ohms
Sec 10K CT ohms
Max DC 30mA
 
Mfr's part#: 6W68HF
Allied Stk#: 227-0862 

$15.06 Each

http://www.alliedelec.com

[WBear2GCR]

Bear,

<snip>

If you dont plan any really heavy modz to the modderz, and still plan to run them AB1 with no grid current, just about any 3:1 step up interstage will work just fine. If you got something close in the junk box, give it a try, it will prolly work.

And.......er.....furthermore....... If you are planning some descent audio out of the V-2, bulldoze the whole audio section out and do the 12AX7 / 6C4 thing!!

                                                                   The Slab Bacon

Yo Frank,

That's gotta be AB2 stock, unless the driver stage simply can't muster the snot to drive the grids positive... which is possible.

And, I think I'd not use a 6C4, but a pair or 12AX7 might be nice, and maybe run the driver tranny in p-p on the primary, and get the DC offset off the primary... but actually the way to go is with a "parafeed" onto the primary. That's what audio people call a modified "Heising" coupling to the primary of a transformer - a choke on the plate and a cap driving the primary. Works nicely, improves the highs and lows.

As I said, it is some sort of cosmic conspiracy at work.

             _-_-bear

[WBear2GCR]

Has anybody tried a 1:1 transformer here?  It seems as though a lot of designers went with 1:3 primary to secondary ratios, but in the Viking II it looks to me like a 1:1 would work OK.  I took the 807s out of my Viking II and put in 8417s with cathode follower drivers and no driver transformer, so I don't know.

Allied Interstage Audio Transformer
Pri 10K ohms
Sec 10K CT ohms
Max DC 30mA

http://www.alliedelec.com

Wait a sec! Hee hee.

That's approximately the same ratio as the stock transformer, because each half of  secondary is 1/2 of the turns, which when looked at as an impedance is not half. So, iirc the ratio there is 10K pri to 1.4k per 1/2 secondary winding. N1/N2 = sq rt Z1/Z2.

I think the Hammond spec shows (2) secondaries, and specs the impedance ratio per secondary. It's up to you how you configure it.

At least that's what the formula seems to say... unless I got lost somewhere in there.

               _-_-bear

[W1GFH]

This guy modded the step-down configuration...

http://members.cox.net/n4jk/viking_ii.htm

[WBear2GCR]

Yeah thanks, someone sent me the link to the N4JK page via email.

I think I have a 100% kludge workaround but I probably will not know until next weekend if it will work in the actual unit or not. I tried it on the bench, tested that is, and it looks quite ok, good freq response.

I'm sure it will make audio, but how much and how good remains to be seen.
I'll post pix once it is in place and working. And share the yuks...

No luck on the local source, he had the 124E model only. 

My best audio friend is out of town until Thursday - at a Boy Scout thing with his son.

Soooo... my kludge transformer concept will get transplanted in.
Then if the conspiracy to keep me off the air continues, something else will fry, or be intermittant and impossible to find... but I hope not.

Local audio & ham friend W2FFC, John suggested a complete rip out and redo, which we landlined the discussion for a while. His idea was to "preserve the chassis" by mounting the new toobes and parts on an "L bracket" mounted via existing holes rather than blasting and drilling. If the stock circuit with the kludge performs ok, and/or a suitable replacement transformer appears as if by magic it probably will stay stock for now. But if the kludge fails to perform, there is a definite chance some other tubes will appear on a subchassis mounted over the spot where the two 6AU6's went...

Ya gotta love it! 

              _-_-WBear2GCR

[WA1HZK]

Junk the transformer and rewire it for a phase splitter. This same ckt. should work for driving 807's just as well as 6146's or the 6J5 tubes I used to drive my 845's. This is what I use for all my Johnson and Heathkit audio conversions. Uses no iron at all.
http://www.criticalradio.com/833%20Rig%20Project/Pre%20Amp%20-%20Phase%20Splitter.jpg

[The Slab Bacon]

Bear,
       The original config is AB1. A 6AU6 doesnt have enuff snot to push the 807s into grid current using a step up driver transfoma.

Try cascaded 12AX7 for mic amp / speech amp, and a 12AU7 with both sections in parallel for the driva. (ala ranger / valiant) this setup works pretty ok-fb!! It also has enough ba's to push the 807s into AB2.

                                         The Slab Bacon

                         

[WBear2GCR]

Frank,

That's interesting, because I really didn't know what the Ranger and Valiant were using, but that was pretty much what I was thinking, but I'd go p-p on the primary side if I was going to go that far with it. Get the DC off.

Didn't think the 6AU6 had the requiste omph...

HZK, two problems with that circuit for me. I prefer to run the output tubes in "2" not "1", so cap coupling is not my fav. I'd run cathode coupled to the grids if I wanted to dispense with the iron... and that circuit as shown is set up for 600ohm in, driving the cathode of the inpoot. So, it'd have to be changed to provide enough gain for a mic input.

As I said at the top I really wanted to avoid modifications if possible and just get the rig up and on the air.

                    _-_-bear

[The Slab Bacon]

Bear,
       I've used the parallel 'AU7 and 124D transfoma to drive P/P 6L6s, 807s, 2E26s, and 6146s and neva had any problemz. If you want a really strapping minature tube for a driva, you might also look up the spekz on a 12B4, they also make a good driva for smaller tubez wanting to see some grid current. (12v fil is center tapped to run on 6v)

                                                   The Slab Bacon

[W7SOE]

While you are in there you may want to consider the elegant mods described by K6AD in a two part article in ER magazine.  (issues 110-111 I think...)

Rich

W7SOE

[WBear2GCR]

Rich,

Don't have any ER mags here, 'cept for one and that ain't it.
Wonder what the general circuit idea is/was??

Slabaco, very familliar with the 12B4 - strapping tube on steroids.
And I have no doubt that a paralleled 12AU7 or 12BH7 etc. will drive the snot out of them leetle modulator toobers! 

Weeelll, a good samaritan lurking here has offered to send me a gen-you-wine Viking xfmr to feex da reeg!! Yay!    So, that problem is solved!!

If it goes together as expectadoed, and the changing of the caps and transplanting of the low B+ iron works, then I'll see how the audio section measures for freq response and see how it drives the 807s. Then I'll get to decide to slash and burn the audio section and put some ^manly[/i] toobes in to make it sing... first get it on the bloody air!! 

                   _-_-bear

PS. Beware of the master conspiracy!!

[WD8BIL]

Here's the scoop on the 12AX7/6C4 mod Bear. I gots it in both the Viking Bud and Viker 2 as seen on WD8BIL.COM.


Viking audio mod

Tons of gain at the input. I actually hook a .1uf to the top of the pot for line level in. WAYYYY too much gain at the input for an audio board output.

Enjoy. Mine have been very good rigs.

If I can find it I'll post the 2ZM 12AU7 phase inverser used in my Viker 2 when that interstage crapped.
The viking one has the 156 tranny from AES previously mentioned.

[N3DRB The Derb]

I seem to rememeber drilling a xtra toob socket for a 6c4 in between the existing sockets, usin a internal gain control between the 6c4 and a triode connected 6aq5. once set, blasted the snot out of those 807's. I used the 40 ma AES driver xfmer. damn that was over 20 yers ago.

[WD8BIL]

AHH Yes Derb........ drillin' n blastin' ....... big time hamming !!!

I didn't hafta D&B on the Viking 1 for the 9 pinner for the 12AX7. I guess the socket I found was a fluque !

I did hafta ream out the mike amp 6AU6 hole on the Viker 2 though. I think it took all of 30 seconds. No biggie.

Good luck Bear. Lotsa options. Make it your own man !

[The Slab Bacon]

A step drill (unibit) is great for "stretching" tube socket holes!!

[N3DRB The Derb]

I am a firm believer that 80% of how good or how ba a rig will sound happens in th first two mic amp stages and the driver stage. ither go with quality iron or phase split the audio into P-P as soon as possible. My entire driver setup with the HB rig was P-P from the first tube back. Think the mi mp was a 6SN7 or a SJ7. Had a high gain pentode section and a low gain triode where the splitting got done.

I designed that entire audio deck from scratch. No yearbook schematics. was P-P from the first tube all the way to the 2A3's. My one modern concession was fixed 5Watt Zener bias at -62 volts. Damn thing worked first time I turned it on n never broke once.

[The Slab Bacon]

And sounded good too boot!!

[flintstone mop]

Let's try a different approach...........ditch the transfromer and with about $12 worth of parts go with the direct method. Using a phase inverter. You can still apply bias if needed. ER mag has a few circuits out there to eliminate the nasty transformer
Fred

[WBear2GCR]

Well I put up the "cheesy" message icon, because I had no idea which one that would be...!

I'm a gonna make a run at it over the next few days and see where I end up. If the conspiracy holds, then something or other will be sure to make certain that the rig is not and can not be pooton deaire. Beware of those alligators, once you have an infestation of them, they are very difficult to rid urself of! Round here they are everywhere, but are stealthy and in camo in all seasons. Can't see them. But you can see the results of their sabotoge! Like ants they are - kill one, and a dozen come back at you! beware!

Guarantee that they got to that Viking!

         

                     _-_-WBear2GCR

PS. they got to my D-104 too! Suddenly sounds like a tin can!! Resistance is futile!
Aaaaaarrrrrrrrrrrrrrrrrggggggghhhhhhhhhhhhhhhhhhhhhh!!!!