Tweed Deluxe 6l6 OT options

[haricros]

Hello,
I'm looking for builders to share their opinions on the following Output Transformers for use in a homebrew Tweed Deluxe with 5881/6l6s:

MM - Tweed Pro OT
MM - Tweed Deluxe dual Primaries OT
Heyboer/MOJO - Tweed Super/Bandmaster OT
Triode Electronics - 35 Watt Dual secondaries OT
Mission Amps - Tweed Super OT

Other options?

I'm looking for something to give a bit more headroom. I'm currently running on a MM Tweed Deluxe OT, Tung Sol 5881's, 5V4, a 30 Watt Weber Blue Dog, and the other mods suggested in previous threads (1K grid resistors, 270 Ohm/10 Watt bias resistor, 2.7K and 33K dropping resistors).
Thanks,
Darcy

PS - anyone have specs on the MOJO/Heyboer OT? How many taps are on them?

[TD_Madden]

I'm using a Tweed Super trannie (actually I got it before he offered the Super kit) from Mission. VERY big sound with a 10-watt bias resistor, his volume/tone mod, and the Paul C mod.

Using a Reverend 12-inch, a CopperCap GZ34, and a 12AX7 in the first socket.

EXCELLENT volume and harmonics; easily keeps up with my Super.

[elpops]

I have some sort of tweed Super OT from Bruce that lets me run 6V6 or 6L6 tubes. The 6L6 sound is stronger, cleaner, and more defined, but not necessarily that much louder. Maybe just a little.

[sjhust]

6L6 _or_ 6V6, with choke?

I've been going back and forth since January trying to decide how to build my 5e3, and now I have iron, so it's fixed (almost).

I've got (as in I ordered, paid for, and took delivery on) an MM tweed dlx dual secondary output, a deluxe "fat stack" power, and a Super-size choke. I'll be using a Hoffman board. The mains transformer is 350V ct.

So for 6V6 and a choke, I just replace the 5K dropping resistor with the choke. But this will increase the B+, right?

And for 6L6, there are 2.7K and 33K dropping resistors. Is it at all possible to have a choke in the power supply, and supply either 6L6 or 6V6, without having to use a switch? Obviously the rectifier has to be changed.

steven

[Amp Kat]

350 vac will put you at about 500 volts after rectification and that's to much for 6v6's but 6L6's would work fine if the output tranny is capable of handling the wattage which sounds like it is. Most Deluxes run the 6V6's at about 420 vdc so you may have to come up with a regulator or some type of back bias circuit to drop it some. Other than that sounds like it would be a great amp.

[sjhust]

Ok, now I'm going to ask a very stoopid question. Be patient with me.

What is "back bias?" I have my suspicions, but I'd rather know.

Paul at MercMag sold me the trannies as a set, so I'm going to assume he knows what he's doing and the output will handle it.

Never mind I found the explanation on the Aiken site. But I have to drop 80 volts, and I have to make sure the switch that cuts it in is robust enough. I'm going to have to put my thinking cap on.

steven

[Bruce / Mission Amps]

In this application a 350vac PT with a NOS 5R4 tube should drop your VDC down to less then 450vdc under a modest load.
With a pair of cathode biased 6L6s idling at around 40ma-50ma each, I think your 350vac tranny will be loaded pretty good and the actuial B+ will be less then 450vdc anyhow.
From there you can use a string of 4 or 5, reverse biased, $1.00, 5w zener diodes in the PT's high voltage secondary center tap.
Keep the voltage of each zener diode lowish, like 10-12v.
That way the constant current across each diode's 10-12v drop will not generate too much heat for the diode to handle.
EX:
120ma draw across a 10v-12 drop = 1.2 to 1.5 watts.
A 5 watt diode is safer this way.

[sjhust]

Thanks, KB, thanks, Bruce.

Between this and the Aiken page, I'm beginning to understand it.
For the 6V6s, I have some NOS Sylvania 5Y3GTs I was planning on using. For the 6L6, I was undecided as yet.

I am a bit confused now about the PT HV secondary. The transformer is a Deluxe Reverb transformer, which means it is intended for 6V6s and a GZ34 rectifier. MM sells Tweed dlx transformers with up to 380 CT, for 2 6V6 w/5Y3. I understand that the ideal rectifier would give close to 500V, but tube rectifiers cause a voltage drop of various sizes. Now, what point am I missing? I understood from all I had read, that I could use this transformer for both 6V6 and 6L6 if I change the rectifier. Or is it the choke that is going to screw things up here, because I don't have the 5K dropping resistor in there anymore? Should I use the choke _and_ the 5K (or 4K, or whatever) to make sure the voltage gets dropped enough?

I have the feeling that I _almost_ understand what is going on, but am missing some last vital bit of knowledge which is going to cause everything to blow up.

steven

[PharmRock]

6v6 and 6l6 switching with dual primaries OT

Hello all...
First-time poster and novice amp tweaker here. I came across this thread and it seemed like an appropriate place to post my question even though this thread is a couple of years old.

I recently purchased a 5e3, but it was built to run 6l6 tubes. It is a fixed bias amp currently using a MM OT with 6K primary and 8ohm secondary (FTWPRO-O). I am toying with the idea of getting a MM dual primary OT (FTDO-59M) so I can have the option of matching correctly with either 6v6 or 6l6 tubes and change between the primaries by using a heavy duty DPDT switch. The PT is a FDP-20.

I understand that 6L6's run higher plate voltages compared to the 6v6, but I've read on various forums as well as the Eurotubes site that the JJ 6v6 can handle plate voltages up to 450v in triode mode and 500v in pentode mode.

This leads me to believe that I can easily pull the 6l6, flip the switch to the 8k primary, plug in the 6v6 tubes, turn the amp back on and let idle for a little bit, do a quick bias adjustment, and be on my way. If I want to go back to 6l6, I can still do that with a flip of the switch and a bias.

I have not measured any voltages yet.

Am I missing something here? I suppose a recto tube swap would be in order as well? It currently has a Ruby 5AR4.

Again...I'm relatively new to all this. I've "trained" myself by doing extensive mods to my Valve Junior. I've learned enough that I think I know what I'm talking about, but in reality I'm just more dangerous than I was before

Thanks for your help.

[Bruce / Mission Amps]

If it is a fixed bias amp (fixed bias: power tube's cathodes grounded and a negative voltage supply built to apply this negative voltage to lugs 5 of the 6V6/6L6 sockets)... then you can keep the 6K output tranny.
Run the 6V6s with a softer rectifier, such as a New Old Stock 5R4 (not 5AR4) or the softer NOS 5Y3GT.
Set your idle current by adjusting the bias supply so the power tubes are idling at around 10 watts each.
If you don't know how to do that yet, there are lots of threads here on AMPAGE describing how to do it.

[PharmRock]

Thanks Bruce...
I have dialed in the bias on my valve junior by swapping out resistors(cathode biased), but the fixed bias seems fairly straight forward (and much easier).

I appreciate your feedback on this. I was thinking that the 6K would be "close enough" for impedence matching with the 6v6, but wasn't sure.

It doesn't seem like I need to do much more than a tube swap and a simple bias adjustment, which I guess is the best case scenario.

thanks again!

[PharmRock]

limited bias range

I finally got around to doing the 5y3/6V6 swap. Unfortunately, I ran out of knob when trying to bias the 6V6's...I could only get to about 20mA.

Here are my numbers...first are what I had with the 5AR4 and 6L6's:
Pin 3: 460v
Bias: 38mA

When I swapped out the 5AR4 with the 5Y3 (Tung-Sol 5Y3GT/G) and put in the 6V6 tubes, I measured a plate voltage of 435. So I figured that, in order to get a bias of 10 watts, I needed to set it at about 23mA (Bruce....was your recommendation of 10 watts based on 70% of 14 watts for the 6V6?). Anyways...this 23mA seemed pretty low for a 6V6 from what I've read, and I thought I might be able to go up to 26mA if I needed to and be at about 80% max. So...I started turning the bias pot and maxed out at 20mA.

My question is...now what? Should I change the resistor that goes from the bias pot to ground (currently, it is 4.7k). When I put the 6L6's back in and re-biased the amp, I noticed I could sweep from 7 or 8mA all the way up to 56mA. Would changing the resistor to another value in order to bias the 6V6 still allow me to effectively bias the 6L6 within its normal range (~38-42mA?).

BTW...I have JJ 6V6S tubes, which I've read can handle pretty high plate voltages.

Thanks for the help! Sorry for so many questions...I'm learning as I'm going.

[tubeswell]

Assuming your bias pot is wired as a variable resistor in series with the resistor to ground, then if you want a bigger range on your bias adjustment to handle both 6V6 bias range and 6L6 bias range, then put in a smaller fixed resistor and a bigger value pot. Then you will be able get a bigger range.

[PharmRock]

6v6 and 6l6 bias

Tubeswell....

yes...the resistor is in series with the bias pot. I don't know the value of the pot, though. Since the resistor is a quick swap compared to the bias pot (and I already have some resistors around), do you think that just changing the 4.7K resistor to something a little smaller would help out any?

Also...do you think that I need to drop the plate voltage down more? With the 5Y3, I'm running at about 435 (previously 460 with a 5AR4). With such high plate voltages, it seems like my bias setting will be too low for 6v6's. I'm using the formula below to calculate the bias:
(10W / plate voltage) *1000

Obviously the higher the plate voltages, the lower the bias setting in mA. From what I've read, 6V6 should run around 30mA???? Based on this, I need to get the plates to around 350? Not sure how I can do that unless I changed the power supply resistors, which I don't want to do because I would like the ability to go back and forth to 6L6's with a simple recto swap and bias adjustment. Maybe my head is in the clouds and this can't be done.

Is there another recto that could be used to drop a few more volts?

Thanks again for everyone's help.