Getting KT66s into a Tube 120

[GaryMadore]

Heya,

Some of you may have seen the major surgery I just did on a Vypyr Tube 120 in order to top-mount the tubes and space them out enough to fit some KT66s.

I had some concerns about the power transformer's ability to handle the current draw of the big bottles:

6L6's draw 900mA each for the heaters, plus 300mA for the 12AX7 for a total of 3.9 amp draw on the 6.3 volt tap.

KT66's, on the other hand, draw 1300mA each, plus 300mA for the 12AX7 for a total of 5.5A draw on the 6.3V tap.

That's an increase of some 41% and, as it turns out, well outside the capability of the power transformer in our beloved '120s.

There was a guy here who modded his 120 to handle KT66s but he hasn't been on the forum since 2013... I have no idea what tubes he used, if it worked, etc., etc., etc.

I was discussing this with a friend of mine who happens to be an Electrical Engineer and we were kicking around the idea of replacing the PT with a beefier model designed to handle that 5.5A draw.

Then we hit on the solution: Add a (third) transformer dedicated to the heater circuit and just not use the stock transformer's 6.3V tap (or use it to power some LEDs and a cool jeweled power lamp or fans or whatever.

I could use the Tung Sol brand KT66's, as they only draw 900mA each, but the whole reason behind this entire project was to take the Big Vyper and mod the hello out of it until it's a true Frankenamp.

The guys with the Vypyr 60's seem to be doing OK with their big bottles. At least one of them is running Tung Sols, though, so the draw isn't an issue. If someone is getting away with another brand of '66's, they are likely enjoying some success because the 60 only has a pair of 'em, so the increase is only 800mA and not 1.6A like it is with four of 'em. We did the calculations and if I try it I am guaranteed to have a shorted transformer in pretty short order.

So, I'm gonna go for it, and install a third tranny. Go big or go home. In for a penny, in for a pound. A bird in the hand is worth two in the bush. OK, that last one doesn't work...

Anyway, I'm going to set this thing up to run a quartet of Gold Lion big jugs - and I started this thread because I know that there are others out there who want to do the same thing. I'll document the procedure, things I find out along the way, and then photos of the resultant smoke and flames for everybody to giggle at.

Wish me luck....

Cheers!

Gary

[dalrymple]

If it does blow, it will be epic! And EXPENSIVE! Dont Fu*k up!
Dalrymple

[GaryMadore]

If it does blow, it will be epic! And EXPENSIVE! Dont Fu*k up!
Dalrymple

I'll be sure to have the video rolling

G

[GaryMadore]

Step One: I ordered two NOS Hammond transformers last night. Both are 6.3V output, one at 6A and the other at 10A. Both have plenty of snot to light up those big-draw big-bottles.

I'll disconnect the stock power transformer from the heater circuit (easy-peasy: two yellow wires come out of the PT and connect to "spade" connectors on the PCB) and connect a new, third, transformer to the PCB using those same spade connectors.

The stock PT's 6.3V tap will either be insulated/wrapped and stowed, or perhaps used to power something cool. We'll see.

With a little bit of luck (and a lot less snowfall), I should have the new trannys this week.

Cheers!

Gary

[dalrymple]

Well at this point I gotta say you got more than big bottles. Cant wait.
Dalrymple

[GaryMadore]

Well at this point I gotta say you got more than big bottles.

I see what you did there

G

[GaryMadore]

The problem: You want to put BIG jugs in your Vypyr Tube 120 but you did the math and determined that your stock power transformer can't handle the extra 1.6 amp draw on the 6.3 volt (filament) circuit.

The solution: MORE POWER! Arr, arr, arr, arr (in best "Tim Taylor" voice)

I called Scotty down in the engine room but he said he couldn't help and mumbled something about dilithium crystals.

So I went with the next best option and ordered 11 pounds of iron in the form of a couple of NOS Hammond power transformers. These Canadian-made units are both dedicated filament power supplies and provide 6 amps (the 267X60) and 10 amps (the 1129X60) on a 6.3 volt tap.

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I haven't decided which one to use yet. Both will do the job, but the big 10 amp block o' steel will do it and run cooler while doing so. We'll see.

At this point I'm only worried about two things:

- the lights in the neighborhood dimming when I power up the amp; and

- ever having to move this thing: it was heavy enough before adding another tranny.

Surgery is scheduled for tomorrow....

Cheers!

Gary

[dalrymple]

I can see the arcing of a Tesla power grid; Lightning in a bottle, sparks flickering out, definitely lights dimming in the neighborhood. Good ol' Canadian Bacon... MMMMmmmm, and a HEAP-o-it. You have entered the certifiable zone, and I only hope the results match the effort. I cant wait to see the pics of the gold lions and hear your impressions of your post apocalyptic rat rod of a futuristic amp. It is a hot rod in the truest sense. Early 21st century technology, beefed up by a power tranny from the 80's converted to a new task. What kind of wheels are you going with?

I'm a car guy and I know. Hot Rod.
So, how fast you think she'll go?
LOL! Dude, you got issues. Are we not entertained?
Dalrymple

[GaryMadore]

You have entered the certifiable zone

IKR?

rinR4GART.jpg (148.41 KiB) Viewed 6177 times

Cheers!

Gary

[GaryMadore]

Bad news: NOS (read "antique") transformers are risky.

I took 'em out of the box and noted that the fabric covered wires were very stiff and that the fabric itself was very brittle. It was cracked in places and looked shaky so I took a bunch of heat-shrink tubing and set about sheathing the wires (over top of the fabric insulation) with it.

That done, and being the prudent dude that I am, I thought it best to bench-test the transformers before letting them anywhere near my amp....

Uncle D, you would not/NOT have been disappointed: There was much arcing and LOUD buzzing/humming, tripped circuit breakers, and a blown fuse in my multimeter. Sorry there's no video, but I was too busy diving for cover while trying to yank the power cord.

It's pretty obvious that the varnish on the windings has long since disintegrated, leaving the primary shorted. Bad ju-ju.

On the bright side, the two old Hammonds will make AWESOME bookends....

I bit the bullet tonight and ordered a brand-new 10 amp Hammond from Mouser. Stay tuned...

G

[dalrymple]

Oops. Sorry, dear.
Dalrymple

[GaryMadore]

Oops. Sorry, dear.
Dalrymple

Heh... pretty much.

On the bright side, it melted some of the snow out back; I can see my BBQ

On a happier note, I finished the cabs today. Head is done except for the etched (PV logo) glass....

The new transformer will be here this week and I can get back to the lab... mwahahahahahahahaaaaa

Cheers!

Gary

[GaryMadore]

OK, so...

I've already babbled about how I went about relocating the octal sockets (as well as the nine-pinner for the 12AX7) in order to space 'em out enough to make room for the big glass (and to move 'em up top so I could "bottom-mount" the chassis in the cab I built for it). I won't bore you with that stuff unless there's a question...

The new transformer arrived last night and I got to work with an incremental approach.

First order of business was to set up the new transformer with appropriate terminals: Spades on the 6.3V filament circuit, ring terminal on the center tap (CT) so it could be grounded, and tinning of the input (primary) leads for the eventual splice into the power circuit.

Next was to bench-test the new transformer. I applied 120V AC to the primary with the secondary's CT grounded and a meter across the 6.3V leads. No smoke, no flames, no buzzing or humming, nothing scary: Just a stable reading of 7 V or so (analogue meter with a needle display (!))

The following was all completed with the amp on Standby (no power to anything other than the heater bus):

After the bench, the next test was to see if the 120V supply to the amp could support all of the transformers without blowing a fuse. I temporarily connected the new transformer's primary inputs in parallel with the existing power transformer's (PT) leads on the power PCB spade terminals and turned on the mains power. Again, nothing bad, and a steady 7V reading on the meter.

Next step was to see if the new transformer could actually power the filament bus on the PCB. I disconnected the existing PT's heater leads (the big yellow ones) on the main PCB and plugged in the new transformer's leads in their place. A flip of the switch, and... no popping, smoking, cracking, was observed, AND the amp's infamous "light show" came on.

Next was to permanently splice into the AC power. Yep: Cut those wires -AFTER the master power switch- and splice in the new transformer's primary leads. Scary. A quick test and, yep, everything seemed OK. At this point I mounted the new transformer on the chassis with #10 sheet metal screws.

Next I dug out 5 old/backup tubes and installed them. A flip of the power switch and I was greeted with the welcome glow of brightly lit filaments. The new transformer took up the load and was now successfully independently powering the bus without complaint. Note: One upside of this is that the old PT will now run cooler, much cooler, because the load is way reduced.

So far, so good.

OK, show time: I took out the old tubes, installed the Sovtek 6L6s I bought a little while ago, reinstalled the chassis in the enclosure, plopped it on top of the 2x12, powered her up, watched the tubes come alive, plugged in a guitar, took her off standby, and listened.... nothing. No hiss, no hum, no bad ju-ju. Rolled on some volume and was greeted with the sweet sound of a Stratocaster pumped through a clean Fender Twin. Pure Audio Bliss.

Since it all worked, all that remains now is to order the Gold Lion KT66s and pop 'em in when they arrive. The heater load requires just over 5 amps and the new transformer can kick out 10 - so there won't be a problem.

It... Is... ALIVE!

Recap:

1) Relocate the sockets in order to make room for the larger tubes. You can move all 4 like I did, or just relocate two (1 and 3 or 2 and 4) - either will work. Because I wanted radical changes, this entailed soldering 41 wires to the PCB where the sockets used to be mounted. There are MUCH easier methods and I am working on one now for a member here to test out.

2) Get a transformer that will provide at least 6 amps on the 6.3 volt tap. Options include a whole new, beefier, power transformer or (like I did) a third transformer dedicated to the heater circuit. The 10 amp Hammond I got from Mouser is small and affordable and does the job.

3) Splice the new transformer's primary leads into the extant Power transformer's AC input (the blue "Transformer Neutral" and black "Transformer Hot") wires that come off the small power PCB at the rear of the chassis. It doesn't matter which lead from the new transformer goes where (despite the "neutral" and "hot" markings on the PCB).

4) Disconnect the current power transformer's heater circuit (two yellow wires) from the main PCB and connect the new transformer's 6.3V supply. Again, it doesn't matter which goes where: we're dealing with AC here.

5) Ground the center tap of the new transformer to the chassis.

6) Fire it up.

Note: If you go with Tung-Sol KT66s, you can skip steps 2-5 I would have done this but the mad scientist in me demanded a more complicated procedure.

I'll add some photos later...

Cheers!

Gary

[GaryMadore]

Pictures to accompany the narrative above:

The new wires soldered to the PCB and ready to solder to new sockets:

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New mounting bracket fabricated from a strip of aluminum. There is also a (narrower) strip of aluminum to mount the front of the transformers:

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New sockets wired up and in place:

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Everything put back together:

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The chassis back out for more surgery. New transformer to the left. Note the cool new spring retainers ready for KT66s:

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The power connectors you need are the two partially obscured spade connectors at the front/left of the small power PCB:

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The filament (heater) connectors are the two spade connectors at the back/right of the main PCB:

Tube063.jpg (1.11 MiB) Viewed 6101 times

New transformer installed and wired. It's not clear from the photo but the primary (black) wires are spliced into the main power supply, the 6.3V tap (green) is connected to the heater bus, and the 6.3V center tap (green/yellow) is grounded over on the left near the output transformer and new output jack. You can see the two yellow wires from the main transformer have been removed from the PCB. They were taped and stowed before putting everything back together but might be used to power something cool, maybe some LED lighting or a cool power "jewel" light:

Tube059.jpg (949.08 KiB) Viewed 6101 times

That's it. It seems easy when reduced to a couple of paragraphs and photos, but I have to admit that I struggled and sweated. A little

If anybody wants to try this and has questions, feel free to ask here or via PM.

Cheers!

Gary

[godoy.rafa]

Awesome... But can you put some valves in my VIP 2???