The AM Forum

I purchased a 'Valaint' years ago from a well known Amer. It was ok but unfortunately it had a serious 60Hz hum. After replacing the PS and electrolytics in the speech amp to no avail, I decided to gut it from the modulators back because there was some modifications done that I wasn't quite familiar with. So what I am left with is a pair of 6146B's as modulators and the regular 6146s in the final. I don't feel quite up to 'Turbocharging' it like Frank, WA1GFZ has done with his but would I benefit using his MOSFET speech amp or going with John, WA5BXO's modest transistor driver directly to the grids? Granted John's speech amp still requires a first stage but other than that it seems similar. This project started out with doing the Timtron mods but as they say, "Life gets in the way!", and I lost track of where I was at the point of restoration. Advice and criticism is greatly appreciated.

Hi Mike,

Let's see.... maybe I can give you some ideas to ponder -

You could strip out the rest of the audio and make a "SummerBreeze" version using the 85W SS amp and a big Hammond 1642SE transformer.  That should modulate well.

Or, you could use the 6146 modulators with regulated screens and grids and drive them with a  GFZ MOSFET  audio driver board.  Maybe find a multimatch mod xfmr or something better or equiv.

Or change the modulators out for some strapping sweep tubes and a better mod xfmr.  Use the GFZ SS driver board.

You could even convert the Valiant over to PDM like Frank did to his Viking I rig. But that is a lot of work too.

Or, you could series modulate the 6146s using a pair or three 4D32s. No transformers at all.  Follow the plans I laid out when I built my recent 813 series modulated by a pair of 813s on this BB.

Whatever you do, it should be a fun project.  These smaller rigs are quite manageable.

T

I nominate a pair of 4D32s modulating a trio of 6146s.

Can you say POSITIVE PEEEAAAKKKKSSS lol!

Use Frank's audio board.

I was contemplating a couple Gi7 tubes as finals in my V2, but it's probably going to be sold now that I'm in the middle of the O-Chin.  Also contemplated PDM with a couple HV fets as switches.

Now, it's gonna be about 11N90s.  Power on the island is cheaper to make than purchase.  We pull a megawatt plus at work and generate all our own power due to it being cheaper.

--Shane
WP2ASS / ex KD6VXI

 K1JJ said:That's what I was considering Tom. From reading some of what's been posted here on the other thread the Valaint's mod iron seems to be its Achilles heel. I don't have much selection in mod iron. If I could find a CVM2 or 3 that would be the bees knees! I guess I could do the research and custom wind one using some iron here, (that is actually on the agenda for some RCA mod transformers I can't seem to find anymore). However, preliminary discussions says that audio iron winding is considerably different from power transformer winding. I guess I should go one step at a time here with everything in the shack, (I am just bringing it out of hibernation after a 10 year hiatus!).
KD6VXI said:Shane I just bought 2 NOS 4D32's for the Viking I that went soft. Unfortunately, one is quite gassy,(like its new owner!). It wouldn't take any grid drive and turns a nice shade of purple when Ep is applied. I have to order either a neon sign transformer or an igniter transformer and send the gas back whence it came. When I lit the filament, it didn't show any smoke inside  so it is internal gas and not vacuum loss. I would give that some thought if I had a good supply of 4D32's but I will go with the 6146B's for now.

This is what I am looking at since it is not as radical as Frank's circuit, (ok I'm lazy I admit it!). For whatever reason my work firewall won't resolve the WA5BXO's website on qsl.net so here it is for your perusal: https://www.qsl.net/wa5bxo/driver1.html.

I'll post the schematic and the its tube equivalent.

AC0OB has some cathode modulated 6146/4D32 circuits floating around on AMFone. He uses a 11N90 in the cathode to modulate without any iron.

Also wrote an article in ER #359 about it.

Drop him a line.

I plan to build an 811A/572B one if I ever clear the bench of my current projects, just because. I will post my schematic when I get home later.

John

Edit - here is data from Phil and my schematic. My circuit is not at all tested/verified.

Why not just put it back "stock", they sound fine right out of the box, so to speak.

(https://photos.smugmug.com/EF-JOHNSON/Valiant/i-sHqgtzC/0/a857f8e8/L/DSC_3826-L.jpg) (https://mikeharrison.smugmug.com/EF-JOHNSON/Valiant/i-MxrvP87/A)