Darkvoice 336 Transformer Transplant

[SchizoidMan]

Alright so, I got this idea, neat idea (hopefully), after modding my Darkvoice 336 a bit (Hum-Fitz, Better Coupling Caps, Removed the Grid Resistors, 100kohm Pot Replacement, Vishay 25 Watt Resistor Replacement, new Belton Sockets, and soon to replace the 6 bipolar caps with some Mundorfs). Basically I read on a bunch of forums that the heater rails on the Darkvoice are getting excess AC voltage (~7 Volts if your Primary is 120 Volts) and the one solution I've seen is to add a bridge rectifier to the heaters to turn it from AC to DC, knocking it down to ~6.3 Volts (maybe). Basically I've messed with the Darkvoice so much that I've had to rebuild it about 5 times from scratch already, this is my first attempt at soldering and electric stuffs in general using this amp as a test subject (kinda going in hard on this one, 5 shocks in and I finally figured out what a Capacitor does) and I've learned quite a bit working with an amp hands on. Well it was around the 3rd time I opened my amp up to figure out why it was sparking like mad (no clamps to keep the caps fixed, whoops, and yet nothing actually popped thankfully) I kinda went all the way and reached it's transformer. The Transformer is toroidal, designed for a 110 Volt 50 Hz Input (That frequency is my guess as to why the thing is so big, Pic attached for transformer and the wires underneath the PCB) and outputs 135 Volts and 6.3 if it was at 110 Volts (I guess, also makes me think it was made for Taiwan?). So where am I going with this? Well the Darkvoice is cramped compared to other amps, especially actual DIY amps, so the rectifier may not fit and might not even knock it down to exactly 6.3 Volts (I get 120.1 Volts from my home socket), and then I did some research. Well idk how to actually order a custom made transformer, so why not transplant it from a pre-existing transformer with a similar looking build? That is when the Crack came to mind, see I was watching a tutorial about how to solder a Crack Amp, the one with Tyll from InnerFidelity, to get some tips on how to solder, how wiring sockets should be done, and I noticed a small detail in the video, which made me investigate the store page for the amp. See the Amp uses a 6080/6AS7 as it's amp section and a 12AU7 as it's pre-amp and it makes me wonder, if it uses the same Amp Tube Mine uses, and the 12AU7 in parallel gets 6.3 Volts in it's heaters (Wikipedia, hope it's right) which is good for a 6SN7 Tube, and the transformer is Universal from what the buy page says, is it possible that the Transformer from the Crack could be used in exchange with the Darkvoice's Transformer and the amp continues to function but BETTER?

- So Here are my Main Points for the TL;DR:

1. I do not have access to the specs of the transformer, but based on what I CAN see from the tubes it uses, it MIGHT have values that can be used in the Darkvoice (Maybe)

2. Is it Possible to Order just the Crack Transformer to try my theory out, and if anyone would chime in, care to explain any possible Current issues this can bring, since the preamp IS a 12AU7, so the current draw may break the transformer (idk if a 12AU7 is more or less current hungry than a 6SN7, don't want to damage the Transformer after all with heat from excess current, but there ARE adapters for this tube to make a 12AU7 fit a 6SN7 Socket, so kinda hoping it could work out that way, any that can give me an approximation on that please, please do ;-;)

3. If Point 2 isn't possible since selling separate parts may cause info leaks on possible specifications of the Crack Amp, then is there somewhere I can Order a custom made transformer with the right specs for the Darkvoice (Again if anyone can give me a ballpark estimate of what the Transformer's Output Winding(s) SHOULD be for U.S Voltages to make it a bit easier on me when ordering, it'd really be appreciated)

4. The Darkvoice Has a Transformer which has a surrounding metal shell to, I suppose, control the Magnetic flux (or maybe to look nice). If I were to get the Crack Transformer, would it overheat if the metal shell was placed, since looking at pics, the Transformer seems to also be encased, albeit in a smaller metal shell already, or would I have to run the Darkvoice without the metal transformer shell it already comes with (If You've seen a Darkvoice, the shell is the big box with the Darkvoice Logo on it, and dang is that transformer big, probably since it was meant for 50 Hz and not 60 Hz?).

5. This is the MOST Important Point of All, is it even worth Changing the Transformer since the Hum-Fitz Mod effectively removes any issue the high heater rails may cause, since the only one I can think of is possibly tube filament longevity since the prices on Bendix and GEC tubes are so high (And these tubes are getting harder to find too)!

I'm a a bit new at this kind of stuff but I'm kinda learning, since I wanna tackle my La Figaro 339 next, I managed to rebuild the 336 from scratch within it's casing so I kinda feel more prepared to tackle the 339 now, as well as the 336 was kinda the weakest link since it's the pre-amp to my 339. Basically I've gone so far with the 336 that I kinda just want the best for it (What I can afford and what'd actually help the amp of course), so any advice is really great. Also sorry for the post being so long I just kinda wanted to get into detail as to why I'd think it might work out in the first place (maybe).

Anyways Cheers to Ya'll.

[Doc B.]

We don't sell the transformer alone. My hunch is that it would be money better spent to buy an entire Crack kit. It's designed to be worked on, you will learn more of the things you want to learn about how amps go together in the process of building it, and you might even find that it sounds better to you. We can also offer knowledgeable support for our amp, whereas with someone else's amp we have no way to give properly informed advice.

Regarding custom transformers, it's really best to know something of how they are designed and what the specs are that the transformer needs to achieve in the given circuit. Not just secondary voltages but also current ratings, temperature rise, radiated field magnitude, etc. I'd suggest asking Darkvoice what transformer they think you should use to improve their amp.

[Paul Birkeland]

I will add to what Doc B has said that if you take that heater winding on the DV and feed it to a bridge rectifier with a capacitor, it won't quite double the AC current consumed by that winding, but it will be close.  Is the power transformer designed for this?  Only the manufacturer would really know.  Also the 110V issue is common with 110/220V power transformers, which are a common offering in the Asian transformer market.

[SchizoidMan]

@Doc B. Yeah you got a point there, it'd actually be better to just ring up the Darkvoice company, or maybe even the transformer company to get their take, especially since they know the amp/transformer better than anyone, besides, they'd be able to give me the same mounting system as the original transformer too, making installation much less of a jury rig and much safer too. Funny thing is, when I took the picture of the transformer, I noticed the company engraved their website on the transformer for the first time yesterday, even after looking at the transformer quite a lot every time I disassembled the amp, so hopefully they have an English speaking representative/technician I can contact to see if they could consult me on the transformer swap.

Also @Paul Birkeland Yeah the winding current worried me too, that's why I was weighing more on a complete transformer swap, but at least from the pics I've managed to find on a supposed successful attempt at a bridge rectifier for the Darkvoice (Pics Attached), it seems they used resistors to probably reduce the current draw for that same reason, since the amp is literally Input -> Switch -> Transformer -> ~7 V straight to the tube heaters (Pins 7 & 8 on both tubes), so I'd imagine the increased current draw would probably be bad for the transformer if there was no resistance there, although the resistance that I can see is .1 ohm and possibly 2-5 watt on the actual heater In/Out since it seems to be wire wound, and the other resistors I can't even tell their resistance since I can't see their ring colors/name and they guy who did the mod doesn't have the amp anymore to ask the values he used. Overall the bridge rectifier mod worries me since I can't tell what was done exactly to get an idea of how much current I need to drop since the pictures don't have the best angles on the resistors. Other than that he removed the grid resistors and biased the cathodes using LEDs, so I know those aren't part of the actual heater mod.

I mean, I'm leaning towards the Transformer since it'd be much more precisely made for the Darkvoice specifically, especially by the same company who made it and it'd be easier to wire up and safer in general since they'll be able to get me the right specifications, I'll probably call a bit later tonight since it'll be 10 A.M in for them in China, but if I can't get in contact with the company, I'd like to get an idea of how likely the rectifier mod is, based on the pictures. Other than that I'll still change the output capacitors to something with a higher capacitance since I've heard it helps with the low end and reduce the actual frequency cutoff point, although my cans are high impedance so I don't know how much of a difference that'd make from a capacitance increase but they will be higher end caps, and maybe down the line make some CSS loads for the biasing, or maybe wimp out and just use 2 Vf LEDs, since those seem to work fine as well, from what I've read.

Either way, thanks for the advice given, it helps since the better transformer will hopefully increase the longevity of the tubes through proper heater function. Also when I'm done modding my two amps, I might save up and get the S.E.X 3.0 or maybe a Crack-a-Two-a to play around with some more tube types and their wiring. Thanks again for the help and have a good day.

[Paul Birkeland]

That modification looks like it drops the AC voltage going to one tube (which is still AC heated), then rectifies it to feed the other tube.  My experience with seeing this exactl kind of modification is that someone is chasing noise and trying various solutions.  The dropping resistors alone should be enough for you to achieve what you're looking for. 

[SchizoidMan]

Yeah, that makes sense, most noise issues with the 336 usually come from pre-amp tubes not handling the higher heater voltages the first time they're inserted, so it's either 72 hour burn ins, or the more reliable Hum-Fitz mod. I guess rectification isn't necessary since I already did the H-Fitz, I was mostly looking into rectification to make my tubes last a bit longer by stressing their heaters less, although if the dropping resistors are enough then that just saved me a whole lot of time. Thanks for the help and info @Paul Birkeland and have a great day

[2wo]

Have you actually measured the voltage you have on the heater pins with those mods installed?

[SchizoidMan]

  The mods I have done right now are better PSU resistors 10 Watt 2kohm Vishay, 100kohm pot replacing the 250kohm pot, Vishay zfoil 1kohm resistors on the preamp tube grid pins (1 and 4) replacing stock, Belton tube sockets just for the nicer look and less loose feeling tube sockets, bypass caps on pins 3 and 6 (Hum Fitz Cathode) being Elna II electrolytics, replacing the coupling caps to better quality ones (forgot the brand but they're 220uf 450V, replacing 220uf 315V), and Vishay 25 Watt 1kohm resistor replacement from the stock resistors used on the amp tubes cathode.
 
  The next mods are going to be LED 2Vf biasing and replacing the output caps with Mundorf EVO and Mcaps to about 44uf (I'd make it to 60uf since that's the stock capacitance of the output section but the EVO caps take up a bunch of room on the board, although I could stack the Mcaps to maybe fit a third one in, then again my cans are high impedance so 8uf shouldn't really matter much frequency cutoff wise, I hope).

  I checked the Voltage on the Heaters about 2 days ago when contacting the transformer company for the new transformer and it was at ~7V AC, although Paul did give me a good alternative idea which is to simply use dropping resistors, which is a more economic solution, gotta figure out the resistor specs I need though to get the values needed to drop the voltage closer to 6.3V without any repercussions.

  Either way the transformer they're offering custom made has the right specs and it's about ~45$ shipping and all, it may take a while to get here even if I pay for it tomorrow, though I still got a bit of time to weigh my options. The company I'm using is the one who makes the stock Darkvoice transformer so their design should fit the amp size wise as well as spec wise since they are basing it on the Darkvoice.

  I mean I don't think any of my current mods should affect the heater voltage, and from what I measured none of the mods seem to have any effect, so yeah, either I go with dropping resistors or just get a higher quality transformer with the correct specs, either way this mod will just be for longevity of the tubes, although the also reduced voltage may change the sound in some way, if it does hopefully for the better. Thanks for the concern though, but one way or the other that voltage will go to 6.3, I guess it's just how I do it from this point. Thanks and cheers, hope you have a good rest of the day.