Big Bottles in a Mark or Recto?

[GJgo]

Hey guys, I had a bright idea for a project. I penned this email to Mike B. but then I thought I should spot check my thought train with you guys before bothering him. Check it out & weigh in!

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When I got that old 2 channel triple it came with the 6550s in it, which sounded massive, but at your advice we ditched them & put it all back to stock. The amp is amazing after you fixed it up, BTW.

I do remember you telling me that if I wanted to run the big bottles in there I should pull 2 or 4 of them so the transformer isn’t as stressed. I’ve read up on that & it sounds reasonable.

So here’s my project idea- what if we take an old hundred watter, and you mod it to run just a pair of big bottles? (KTxx, 6550, whatever you deem to be the best call)? (Assuming that keeping a quad in there would be too much stress for the transformer.) Should still be what, around 75W output with the pair? The goal would be to capture the big bottle huge-ness.

The potential donors could be either
• My HRG IIC++ with the X101 PT, but the big bottles wouldn’t fit unless I ditched the reverb tank.
• ..Or I could pick up an old 2 channel Dual Recto or Rackto.

Last question, does this sound like it could be a good idea, or it’s dumb & I should forget about it?

 

[paulyc]

Why not try REAL 6CA7s instead ? NOS ones.

 

[psychodave]

What about running the power section in pentode? That will add hugeness.

 

[steve_k]

https://www.eurotubes.com/store/pc/mesa boogie amps.htm

Lots of info on the Eurotubes site.

I would imagine you can run 6550's in EL34 mode with spongy and tube rectifier mode. Put them in there with a bias probe and see what the PV and PC is. I wouldn't do it in a prized pre-500 Recto.

 

[ChurchHill]

Might want to keep an eye on heater current, too. I'm not sure what the max amps on the heater circuit for your power transformer, but if your power transformer has a maximum of 9.0 amps available for the heater winding, you could safely use 3 of the tubes below as sextuplets, but the other 3 would over-stress your power transformer.

Heater Current Per Tube
6550 1.6a X 4 tubes = 6.4a ; X 6 tubes = 9.6a
KT88 1.6a X 4 tubes = 6.4a ; X 6 tubes = 9.6a

6L6GC 0.9a X 4 tubes = 3.6a ; X 6 tubes = 5.4a
KT66 1.3a X 4 tubes = 5.2a ; X 6 tubes = 7.8a

EL34 1.6a X 4 tubes = 6.4a ; X 6 tubes = 9.6a
KT77 1.4a X 4 tubes = 5.6a ; X 6 tubes = 8.4a

Also, something to be aware of is plate resistance. Output transformers have a range of resistance they like to work with. You can go over by a little and be OK, while going below this isn't the greatest idea.

Load Resistance Per Tube:
KT88 4.50k
6550 3.00k

6L6GC 1.70k
KT66 1.30k

EL34 2.00k
KT77 1.05k

Not sure if this helps, and I have no idea what your transformers would be rated for, but I tried to pull this data from old tube data sheets available online. The numbers may vary somewhat between manufacturers.

Edit: I'm not sure how Mesa wires their sockets, but another thing you might want to check is that all the pins on the tubes are wired to what they're supposed to be. For instance, 6L6 tubes have a pin that's disconnected because the connection's internal. EL34s require this pin for its specified use. Sometimes, amp manufacturers will use the disconnected pin of a 6L6 as a "free" connection point for another part of the circuit. If you stick an EL34 in there without changing that, the tube and amp will malfunction at best and blow up at worst. I somehow doubt Mesa does this, but it's always worth it to double check, just in case.

Finally, I agree with steve_k, you should be fine with 6550s running in EL34 mode with spongy selected.

 

[GJgo]

Why not try REAL 6CA7s instead ? NOS ones.

I had a set of Sylvania 6CA7s, also a set of Sylvania 415s. No doubt they were epic but for a wear item, and trying to get good matched ones, and knowing if you're dropping $250 a pair on something that's any good, I can't justify the price for more.

The 6550s that came in the Recto I bought were on a whole other level in terms of huge-ness. At Mike's advice they were just not a good idea to run (all of them).

 

[GJgo]

What about running the power section in pentode? That will add hugeness.

That's an interesting idea. With my Mark IV pentode was definitely bigger in feel than triode. That said, with my IV experience in mind the 6550s were a whole other level.

 

[GJgo]

https://www.eurotubes.com/store/pc/mesa boogie amps.htm

Lots of info on the Eurotubes site.

I would imagine you can run 6550's in EL34 mode with spongy and tube rectifier mode. Put them in there with a bias probe and see what the PV and PC is. I wouldn't do it in a prized pre-500 Recto.

I did an entire test-out with my bias probe in the Recto with the 6550s. Only the coldest settings worked in terms of bias, but that's not the problem. The problem is the heater current is too much for the transformer. Thus my thought of getting a 4 bottle amp & converting it to 2 big bottles, then have it biased correctly for them.

 

[ChurchHill]

There must not be a lot of wiggle room in that power transformer. I rechecked the numbers, this time from JJ, and their EL34 draws 1.5A heater current while the 6550 draws 1.6A. So, 6 tubes, 600mA more with the 6550s. If the transformer's heater winding is already that close to its max, I can see why you wouldn't want to push it.

If you really wanted to use all 6 tubes, you could have them add an additional transformer just to run the heaters from.

 

[paulyc]

Or get a custom spec Mercury or Heyboer power trans to handle it.

 

[Wizard of Ozz]

Buy a Diezel Herbert. Run 6 6550s... 6 KT88s... pick your poison.

 

[ChurchHill]

Herbert ist König.

 

[GJgo]

If I was going to drop 4 grand + on another amp I'd probably order a KT88 Wizard like Reza just got. Short of that, I had my original thought of a converted big bottle 2 channel dual recto as pretty damn awesome for a lot less coin!

 

[CrazyNutz]

Considering you can officially run el34's in a recto, one would think mesa would have used a power tranny that would handle higher heater current.

6550's have the same heater current requirements of el34's. Should be fine on the Power transformer if mesa did their job correctly.

As for 6550's being capable of higher wattage (i.e. 35w per tube), you won't be getting there anyways. You have to have higher plate voltage, and correct primary impedance, etc.

One modification that should be done is to lower the bias feed resistors. When marshall put 6550's in their amps they dropped the bias feed resistors from 220k to 100k. The big glass tubes need more bias current, otherwise they may fail prematurely.

Play the amp a few hours with stock 6l6's. Put your hand on the transformers, (if you have a temperature probe, even better). Then run the amp with the 6550's. If you don't have a massive difference in temperature you should be fine. If they are getting so hot that you cannot hold your hand on it, you may be pushing it.

 

[ChurchHill]

I'll bet a Recto running 6550s still sounds a lot more like a Recto running 6L6s than it does a Wizard or a Diezel. I'd also bet a Mark 2C++ HRG with 6550s sounds more like a Mark 2C++ running 6L6s than it does a Recto, Wizard, or Diezel.

If the 2C++ isn't doing it for you, I'd be looking for something else and not risk blowing the original trannies or replacing them. You could get into a lot of amp trading for that... just sayin'.

If you want something that sounds more like a Recto with 6550s, look at a Twin Jet or an Uber. Used, they're about the price of a used Triple R plus the mod from MB. A used Herbert is considerably less than $4k, too.

And CrazyNuts is right... a 100w Marshall with EL34s will still be a 100w Marshall with 6550s unless you change both transformers and mod the circuit.

 

[Wizard of Ozz]

I'll bet a Recto running 6550s still sounds a lot more like a Recto running 6L6s than it does a Wizard or a Diezel. I'd also bet a Mark 2C++ HRG with 6550s sounds more like a Mark 2C++ running 6L6s than it does a Recto, Wizard, or Diezel.

If the 2C++ isn't doing it for you, I'd be looking for something else and not risk blowing the original trannies or replacing them. You could get into a lot of amp trading for that... just sayin'.

If you want something that sounds more like a Recto with 6550s, look at a Twin Jet or an Uber. Used, they're about the price of a used Triple R plus the mod from MB. A used Herbert is considerably less than $4k, too.

And CrazyNuts is right... a 100w Marshall with EL34s will still be a 100w Marshall with 6550s unless you change both transformers and mod the circuit.

A big +1 to all of this.

... or slave out your IIC++ to a Fryette 2/90/2 or Mesa Strategy 400.

For KT88s, I did like the Bogner Twin Jet I had. It just used some really weird settings.

 

[GJgo]

Thanks guys for helping to keep my line of thinking in check. I'd love a Strategy 400, but Jesus...

I can tell you that when I got the triple & the 6550s were in it, it was an absolute force of nature. Mike just told me it was a bad idea in the big picture. I will say that the 6L6 cut better in the mix, but the 6550s were really addictive. HUGE TONE.

I love my C++, I just have 3 of them. Something different would be cool. Maybe have one of them rewired for pentode..

Kind of a digression, anyone played a Marshall 2203KK with the KT88s?

 

[ChurchHill]

Maybe you could try some KT66s (1.3A per tube), 6CA7s (1.5A per tube), KT77 (1.4A per tube), or E34Ls (1.5A per tube). All are in the heater current range of EL34s and are different than 6L6s and EL34s. I'm still not sure that the heater current is that much higher for 6550s than it is for EL34s (I believe that they use the same amount of current), or at least I'm a little surprised that Mesa wouldn't build in at least a little headroom for the heater winding.

And yeah, a Strategy 400, VHT 2150, or Fryette 2/90/2 isn't a bad idea to get that KT88/6550 sound. Make a killer W/D/W rig, too...

I would agree that the pentode option might be viable, too. Non-invasive and easy to undo.

Sorry, I haven't played a 2203KK... last Marshall with 6550s I played was a stock '78 2203. It sounded good, but I switched it to EL34 the same day I got it. I had 6550s in my Green Uber when I got it, but they didn't last the night, either. Same with my Splawn Competition. I do, however, LOVE the KT88s in my 20th Shiva and I love them in VHT/Fryette's amps, too. I think 6550s sound unique enough that they don't truly shine unless the amp was built for them. I think that about all tube types, but that's just my opinion.

 

[NewWorldMan]

Never played a KK with 88s, but a buddy used to have an '83 2203 that he used with 88s. It was a very slight variation over our 2203s with 34s and 6550s, but not by much. We can tweak all day, tube swap, etc...but an amp will never deviate too far from its core tone unless you're gutting it and making it something different entirely.

I've tried this route before of trying to squeeze a tonal square peg into a round hole and make amps sound like something different. I wasted a lot of time and money going down that rabbit hole, and finally reached the conclusion that when I wanted a different flavor, it's best to just try a different amp rather than continue buying the same ones over and over and hoping for something different. That's just me though, YMMV. I agree with the folks above advocating trying something new.

 

[Racerxrated]

Never played a KK with 88s, but a buddy used to have an '83 2203 that he used with 88s. It was a very slight variation over our 2203s with 34s and 6550s, but not by much. We can tweak all day, tube swap, etc...but an amp will never deviate too far from its core tone unless you're gutting it and making it something different entirely.

I've tried this route before of trying to squeeze a tonal square peg into a round hole and make amps sound like something different. I wasted a lot of time and money going down that rabbit hole, and finally reached the conclusion that when I wanted a different flavor, it's best to just try a different amp rather than continue buying the same ones over and over and hoping for something different. That's just me though, YMMV. I agree with the folks above advocating trying something new.

This....
I had a KK, great amp that hung with the Cameron I had at the time...needed an additional boost though. Great clarity and thump. The only difference tonewise was a little deeper low end, other than that it was all Marshall.