Developing the DIY "Champ" for first time builders

[xtian]

The Edcor OT in the premium package has three wires on the primary side; your layout and schem only show two wires. Please post details.

[ToneMerc]

I am not sure if I can get Heyboer to quote since I can't guarantee them the quantities that they need for a custom wind like this.
rj

RJ, it shouldn't be a problem for Heyboer. They do small 1-2 unit runs for me all the time. I got a 4K, 30W SE, 4-8-16 OT from them last week. However, any of the larger SE output transfomers aren't exactly cheap.

TM

[ToneMerc]

OK Guys - 15 watts should satisfy all but the most sinister of Single Ended beasts... but for some is 25 enough? For those that thought the end was in sight, we have not even talked about the KT-90 and KT-120 tubes! Single Ended doesn't mean we have to build lightweight amps!

rj

25-30W will allow for two 6V6's in parallel as well. I would even try a couple of the small bottle 6L6's with a true 30 watter.

TM

[Travst]

I received my Premium kit yesterday, and everything looks top-notch. Many thanks to RJ for putting the kits together. It's going to be a lot of fun watching everyone building their kits.

[surfsup]

I received my Premium kit yesterday, and everything looks top-notch. Many thanks to RJ for putting the kits together. It's going to be a lot of fun watching everyone building their kits.

Ahhh, I feel like I'm missing out! But I'm sure the Supre is gonna be worth the wait!

[RJ Guitars]

Ahhh, I feel like I'm missing out! But I'm sure the Supre is gonna be worth the wait!

You have been quite patient. Hopefully it is well worth the wait. I do believe we should build things using high quality parts and good building techniques. That generally isn't the fastest method of doing things but I've found that most folks seem to remember how well it turned out, yet soon forget how long the whole process took. This Supre is #1 in the development queue now,

rj

[RJ Guitars]

The Edcor OT in the premium package has three wires on the primary side; your layout and schem only show two wires. Please post details.

Sorry,

I missed this note earlier. The extra wire (Blue/White) is a 40% screen tap. In our amp we don't need that. However, rather than cut it off you might want to just wind it up and tie it out of the way (with no bare wire that can short out) in the event you want to experiment later.

Maybe we can coax one of the Valve Masters to talk with us about wiring up an output tube using an ultra-linear tap.

Also if the Amp Masters don't mind, take a look at my drawing and verify that I am not leading us astray...

rj

[ToneMerc]

The Edcor OT in the premium package has three wires on the primary side; your layout and schem only show two wires. Please post details.

Sorry,

I missed this note earlier. The extra wire (Blue/White) is a 40% screen tap. In our amp we don't need that. However, rather than cut it off you might want to just wind it up and tie it out of the way (with no bare wire that can short out) in the event you want to experiment later.

Maybe we can coax one of the Valve Masters to talk with us about wiring up an output tube using an ultra-linear tap.

Also if the Amp Masters don't mind, take a look at my drawing and verify that I am not leading us astray...

rj

I'm certainly no Master, but you are correct Sir.

TM

[David Root]

Although I've never used one, a UL tap in SE mode could be useful for taming a tube that verges on fizziness in overdrive, without losing any of that even order harmonics generation that SE is all about, at least in MI amps.

UL means ultralinear, and goes back to 1955 or thereabouts when it was a very big deal in audio amps of the time.

What it does (oversimplification alert) is to introduce feedback between the plate and screen. This reduces the output power about 30% compared to full pentode mode, with the 40% tap shown, and gives a tonal character between that of pentode and triode operation.

If you compare the plate curves of the same tube in pentode, UL, and triode connected mode, you can easily see and understand this.

The GE 6550A data sheets from the '70s show this particularly well.

Personally I would love to use two 6550 or KT88 in parallel SE for up to 40W, should still get plenty of warmth even in UL, when cranked. So many tubes, so little time.......!

[RJ Guitars]

Thank you David. I appreciate the way you you said that clearly and simply. Gives us a useful option if not for this amp, one of the many in our plans.

You also tickled another interesting topic in Single Ended amp building - Even order harmonics. So many things to understand and apply.

thanks again,

rj

[RJ Guitars]

Just want to put out a heads up - I am going to be away these next couple weeks. I should have email contact and internet service but I won't be moving any parts out during that time. I have a couple orders that I am working here now that I plan to get out before I leave.

Transformers are ordered for the Supre and I am sure most of you will have your Premium amps complete before I finish the final layout drawings but I am working on those.

I'll have restock supplies coming in for more of the Basic and Premium versions with the thought that I'll keep the parts on hand to do a half dozen kits if anyone gets inspired by your work.

rj

[Firestorm]

Although I've never used one, a UL tap in SE mode could be useful for taming a tube that verges on fizziness in overdrive, without losing any of that even order harmonics generation that SE is all about, at least in MI amps.

UL means ultralinear, and goes back to 1955 or thereabouts when it was a very big deal in audio amps of the time.

What it does (oversimplification alert) is to introduce feedback between the plate and screen. This reduces the output power about 30% compared to full pentode mode, with the 40% tap shown, and gives a tonal character between that of pentode and triode operation.

If you compare the plate curves of the same tube in pentode, UL, and triode connected mode, you can easily see and understand this.

The GE 6550A data sheets from the '70s show this particularly well.

Personally I would love to use two 6550 or KT88 in parallel SE for up to 40W, should still get plenty of warmth even in UL, when cranked. So many tubes, so little time.......!

The amount of output power reduction associated with UL varies greatly with both tube type and the winding percentage of the UL tap. GEC experimented with percentages ranging from 5% to 50% before settling on 20%, but most other designs seem to use 43%. Interestingly, the original patent applications imply that one can expect nearly full pentode output power, though the specifics are lacking. In general, the statement "Sounds like a triode, but with pentode power" is semi-accurate.

UL does dramatically reduce the tube's output impedance which makes its behavior less dependent on the OTs primary impedance, so it sort of eliminates the whole "should it be 4K? 6K? 8K?" debate.

A UL connected tube forces the screen to track the plate voltage (because a percentage of the plate signal impressed on it), so you can drive it a bit harder without the tube going all gnarly when the screen becomes "anodic." Since the distortion-limiting feedback is internal, you can (maybe even should) eliminate the external feedback loop so you don't have both systems limiting output power and impedance.

Real easy to play with. If you don't like it, tape it off. Or get ambitious and make the screen connection and the feedback connection switchable.

[David Root]

Firestorm, thanx for adding that. I had forgotten about the output impedance effect in UL mode, it is quite dramatic, and it is also shown in the GE 6550a datasheet too.

[mike9]

Got my premium kit today - the quality looks great and all the components checked against the list. Thanks again RJ for putting this together.

Is there an absolute last revision for schematic and layout for this project or is it Rev1 that was emailed last month?

[xtian]

Schematic rev 1.2 can be found here: https://tubeamparchive.com/viewtopic.ph ... 225#155968