• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Single Ended Triode?

So I am intrigued by these single ended triode amps... I have been reading about using things like 6l6, 5881, 6v6, and 7591s in triode strapped operation

I owned several vintage 6l6 of various types(including the sexy looking coke bottles), many of them pair matched, as well and a few vintage tung-sol 5881, more vintage 6v6 then I can count and a matched pair of Hammond 7591... hell I even have some 807's laying around

I have PTs ranging from 110v to as high as 3600 volt...

I have more rectifier tubes than I know what to do with...

I figured I could run a pair of fostex fe206en which can be had for around $300-$350 a pair

But i am not sure what would be the best choice for the tube out of what I have on hand?


Crap what do I run for an OPT?

Help me Narrow this down a bit, I am going wild with ideas
 
If you've never built a SE amp, you should check out the Tubelab SSE project. The Tubelab website offers PCBs, schematics, in-depth build notes and detailed reflections on tube and transformer options. The SSE can be built to work with a variety of tubes, can work tube or SS rectification, and can be built to run in pentode and ultralinear modes as well. There is a healthy community of SSE builders posting in threads here : https://www.diyaudio.com/forums/tubelab/
 
6V6 makes a very lovely triode if you don't mind the low power output (1.5~2 watts maybe?) So if you have a bunch of them I would consider going with a pair or trio per channel in parallel. You'll need a strong driver to handle the grid capacitance, but something like a 12AT7, 6N1P, 6DJ8 would do fine.

If you've built guitar amps before you should have no issues really, just a few differences in design philosophy really. Most hifi is more minimalist, no tone controls, biased conservatively, etc.

Here in the US I would look at Edcor USA for output iron once you decide what you want.
 

Duke58

Member
2009-01-03 8:00 pm
Agreed about the Tubelab. I suggest that you start with Simple Single Ended (SSE) board. Everything is well documented on the Tubelab website. I'm finishing a 45 SET amp on a Tubelab TSE-II board and bought a SSE completed amplifier. Using 6L6GC tubes and it sounds really nice.
 
For example???

300B, 2A3, 45, PX4, 6B4G 6a3, etc. There are a handful more oddball types that are cathode types.

I say the better option is to go for a triode-wired pentode, or cathde type triode. Put the money you save into better iron. A nice 6V6 triode will get you 90% of the way to a 45's sound with an easier to use cathode. The 6AV5GA triode wired is very, very close to a 2A3/6B4G, and is also easier to implement.

No reason to stick to expensive dinosaur DHT types unless you just plain want to, which is a good enough reason to use them I suppose. Besides, most are so inefficient for the cost that push pull is a nice option to go with on them for more power and lower distortion.
 

Duke58

Member
2009-01-03 8:00 pm
The OP is asking about which OPT to use, because he has several of the tubes he listed.

Also, buy a Tubelab TSE-II and used the tubes you listed. I'm building a TSE-II with 45 tubes, using Electra Print OPTs. Call or email Electra Print. Or, use Edcor.
 

Duke58

Member
2009-01-03 8:00 pm
"I owned several vintage 6l6 of various types(including the sexy looking coke bottles), many of them pair matched, as well and a few vintage tung-sol 5881, more vintage 6v6 then I can count and a matched pair of Hammond 7591... hell I even have some 807's laying around"
 

6A3sUMMER

Member
2016-06-07 6:50 am
One important decision when using these tubes is whether to use Triode Mode, or Ultra Linear. Not all output transformers have UL taps. UL may or may not require negative feedback.
Pentode mode certainly requires negative feedback, and can complicate a simple amp circuit.

The 5881 is Very similar to most types of the 6L6, except for maximum plate dissipation
23 Watts versus 19 Watts, respectfully.
The big exception is the 6L6GC, at 30 Watts max plate dissipation.
All of these tubes should be able to use the same range of primary impedance SE transformers.
Depending on the circuit, you can tube roll all of the above tubes, plug and play, this is SE not push pull.

The 7591 is lots different than the above tubes.

The 6V6 is not similar to either of the above tube groups.

For SE amps, tube matching is not nearly as important as in push pull. The tubes merely need to have reasonable emission.

For the original poster:

* What loudspeakers are you going to drive with the SE amp?
* Oops, you are using relatively efficient Fostex speakers, right?
How loud do you like to listen?
How big is your room?
What kind of music do you listen to?
 
Last edited:
... Crap what do I run for an OPT? ...

The Hammond 125ESE is an off the shelf, not very expensive OPT. It offers a choice of four plate impedances, four speaker load impedances, and can handle at least 80 ma. I've put over 500 volts through mine without issue.

It's a good OPT for experimenters and will work with all the tubes you have listed. It does not have ultra linear taps.
 
Given the variety and quantity of tubes you mention you have, do you happen to have any 1626s in your accumulations? If so, google: 1626 darling amplifier . . . . for something that might be a simple and fun thing to try, and that received good reviews for its performance, especially relative to its low complexity. I haven't built one yet, but I want to sometime...
 
Given the variety and quantity of tubes you mention you have, do you happen to have any 1626s in your accumulations? If so, google: 1626 darling amplifier . . . . for something that might be a simple and fun thing to try, and that received good reviews for its performance, especially relative to its low complexity. I haven't built one yet, but I want to sometime...


Well hello from a fellow ham in em29sc! I think I might actually have some… But I’m not certain if I’ve tested them when I went to the Dayton ham vention about four years ago I ran into a gentleman who had what turned out to be nearly 250 pounds of tubes... When I first ran into them on the first day of ham fest, I asked him what he would want for all of them and he wanted some ridiculously high number… I replied that I was not willing to pay that and asked him if he would consider a lower price he told me $500… I replied that that was still too much and wished him a good day. On the last day of Ham fast it was raining cats and dogs… I asked him if he would be willing to let them go for $50 so that he didn’t have to load them in the truck in so that he didn’t have to sleep on the couch when he got back home… And then I said something to the effect of because you know your wife is not gonna be happy if you come back home with this crap… Then his wife pops her head out of the trailer and says that boys right take his money and give him that crap and let’s go home… Some of the tubes were new, in fact many of them were new… And a lot of them were used and in incredible condition
 
Well hello from a fellow ham in em29sc! I think I might actually have some… But I’m not certain if I’ve tested them when I went to the Dayton ham vention about four years ago I ran into a gentleman who had what turned out to be nearly 250 pounds of tubes... When I first ran into them on the first day of ham fest, I asked him what he would want for all of them and he wanted some ridiculously high number… I replied that I was not willing to pay that and asked him if he would consider a lower price he told me $500… I replied that that was still too much and wished him a good day. On the last day of Ham fast it was raining cats and dogs… I asked him if he would be willing to let them go for $50 so that he didn’t have to load them in the truck in so that he didn’t have to sleep on the couch when he got back home… And then I said something to the effect of because you know your wife is not gonna be happy if you come back home with this crap… Then his wife pops her head out of the trailer and says that boys right take his money and give him that crap and let’s go home… Some of the tubes were new, in fact many of them were new… And a lot of them were used and in incredible condition

Ha! well done! Given the commonality of the 1626 as the oscillator-driver tube in the ARC-5 transmitters, it's highly likely you have at least a few in that mass'o'tubes. I've been to Dayton a few times in the early 2000s and then in, if I remember, 2007. Hope to go back at some point, but I'm not sure when life will permit that.

I grew up right near Bell Labs and US Army Signal Corps then-HQ Fort Monmouth; all of the old timers thought that it was mighty strange that this 'kid' (then in my teens in the late '70s and early '80s) actually wanted tubes and tube equipment. I wish I now had a fraction of what I passed up, scrapped for components, or gave away. The most grievous regret is about the mint Hallicrafters Hurricane SR-2000 with matching VFO that I could have bought for a few hundred (though that was a lot on my summer job wages at the time). But I do still have some stuff that I thankfully saved, like a really nice, never-issued EAC R390A, a bunch of good condition high quality milspec test equipment, and a fair but not huge trove of tubes and assorted parts. Trouble is that the rest of life keeps preventing me from having much time to do much with any of it.
 
The Hammond 125ESE is an off the shelf, not very expensive OPT. It offers a choice of four plate impedances, four speaker load impedances, and can handle at least 80 ma. I've put over 500 volts through mine without issue.

It's a good OPT for experimenters and will work with all the tubes you have listed. It does not have ultra linear taps.


Well hello to another Ham… It seems there’s quite a few hams on this website… I have looked into this output transformer it seems that it’s rated for up to 15,000 Hz, do we know what the Roloff is after you hit 15,000 Hz? I mean I know it doesn’t just instantly stop producing audio at 15,000 Hz it would have to continue above that I assume?
 
Well hello to another Ham… I have looked into this output transformer it seems that it’s rated for up to 15,000 Hz, do we know what the Roloff is after you hit 15,000 Hz? ...

I know what mine are:

At 1 Khz as the 0 dB point; 1 watt output:

100 Hz was -1dB
70 Hz was - 2 dB,
55 Hz was - 3dB.

The high frequency response is flat to 6 kHz, after which is a very gentle roll off out past 30 kHz. 10 kHz is down about -0.5 dB, 15 kHz is about -0.8 db, 20 kHz is -1.5 dB and 30 kHz is - 2 dB.

edit: I will add that these measurements were taken in a working Tubelab SE, modified to use 801A output tubes.
 
Last edited:
Well hello to another Ham…

Yet, another......Tubelab = KB4LRE, novice call, extra ticket, ham since the mid 80's, although with a few powerful exceptions all of my DIY ham stuff has been solid state, primarily because most of my 41 year career at Motorola was spent as a transmitter design engineer. Free silicon, GaAs, GaN, or SiC beats buying tubes! Truth be told, I have blown up more sand than glass in my life.

I went to the Dayton ham vention about four years ago

I have been to the Dayton hamfest almost every year for the past 15 years, and sporadically before that. What has been the largest purchase every year.....tubes, of course.

I should be there again this year unless $hit happens....yes it can happen....just search YouTube for Dayton hamfest 2011 to see the smelly lake of brownness that erupted in the swap meet lot.

it seems that it’s rated for up to 15,000 Hz, do we know what the Roloff is after you hit 15,000 Hz?

No OPT is perfect. All of them have unwanted capacitance and inductance from the method of winding and types of insulation used. These unwanted effects combine to form a notch in the frequency response curve somewhere in the high frequency region. The depth, width and center frequency of this notch depends on the OPT and the surrounding circuitry.

In a high quality OPT this notch is far above the audio frequency range, 30 to 50 KHz, so that the response is flat to beyond 20KHz.

In a budget OPT this notch can be pretty close to the upper end of the audio range, say 22 KHz. This can cause a gentle rolloff starting in the 12 KHz or so range with -3dB occurring at 15 KHz. The response will continue to drop to maybe -15 dB or more at the point of the resonant notch, 22KHz in this example. The response will then rebound somewhat above this notch, but there will be considerable phase shift causing possible instability in designs that use a lot of feedback.

The previous paragraph just discussed the response of the OPT itself when tested in a fixture designed by the manufacturer, which we know nothing about. Its actual response in your circuit could be better, or worse than what's stated in the manufacturer's data. Why?

We have an unwanted resonant circuit formed by the OPT's leakage inductance, and it's stray capacitance. It is electrically in parallel with the primary and "sucks out" a chunk of signal. Every "resonant circuit," even ones we don't want, have a "Q" factor. We try to maximize Q in most RF circuits to favor a single frequency, but here we would like to reduce the Q as much as possible to reduce the depth of this notch.

We can kill the Q of a parallel resonant circuit by putting a resistor across it, but putting a low value resistor across the primary of an OPT will suck up much of the wanted signal too....but,

The tube that we have driving this OPT has an internal plate resistance. For a big fat triode this plate resistance can be pretty low, 500 ohms or less for a 300B DHT...our budget OPT will like this and it's notch will shrink and move UP in frequency getting somewhat out of our way. Drive that same OPT with a pentode that does not run feedback and it's plate resistance may be 25,000 ohms. Our unwanted notch will have nothing to stop it from stealing all the HF from our audio. Clearly a low plate resistance is desired here.

There is a similar loss of response at the low end of the frequency spectrum. Every OPT has a primary wound of wire wrapped around an iron core. This forms an inductor, and many OPT's will specify this primary inductance. It's directly related to the amount of iron and copper used in the transformer, so SIZE MATTERS. Yes, bigger is better, and bass response of an OPT can be measured in pounds (or kg). A single ended OPT requires a core gap, killing some of our needed inductance, so a SE OPT must weigh about 3 to 4 times as much as a push pull OPT of the same (true) power rating. Again some lack of primary inductance can be compensated for by lowering the driving impedance by using a tube that has a low plate resistance.

We can use a triode, the bigger the better because is has an inherent low plate resistance. We can lower it further by applying some feedback. We can get more power with a pentode, but a LOT of feedback must be applied to compensate for it's high plate resistance. We can also take the pentode and wire it as a triode and get almost as low of an impedance as a triode.

So, pick the biggest triodes in your collection, or the biggest pentodes, and triode connect them.

What do you use for an OPT? Well that depends on your tube collection. You have some 6L6 types. They like a load in the 5K range for SE. Do you have any 6CA7, EL34, 6550, KT88 or similar tubes? They also like a 5K ohm load and a B+ in the 375 to 450 volt range.

Have a bunch of TV sweep tubes? They prefer a lower B+ and a lower load impedance. Many can be triode wired, but the B+ should be 300 volts or less in this case, needing a load in the 3K ohm range.