Transcendent OTL T8 Vs. Atma-Sphere M60

[Brit01]

But if some customs are DIY and read this thread,You can never know....

Lol if they can read English: I'll slip 50 pesos into your pocket! Little persuasion.

I'm using two Hammond toroidal transformers for the main HT supplies for my circlotron; one per channel. Each transformer has a pair of 117V windings, which is just fine for getting the two separate HT supplies.

Surely Hammond, or other, toroidal transformers must be available, via internet order, where you are?

I'm in the middle of nowwhere: Uruguay. Internet shipping for iron would cost a fortune and then customs fees and bribes. In the end I'd be able to buy a ticket to the UK and bring one back myself.

Just power EI transformers here.

2 secondaries: ilimzn didn't like that idea! Lol. I thought 2 secondaries would be sufficient for floating supplies. I'll do some more reading.

You actually only need two transformers, each with a pair of high voltage secondaries

Thxs. good to know. I'll get some custom quotes versus surplus step downs.

 

[tubelectron]

Hi atmasphere,

You might want to take another look at that- if you build a Circlotron properly it is extremely reliable! I've built amps with custom transformers and also surplus parts- the really serious requirement for the transformer is that it be able to handle the current without serious sag as power is increased. Beyond that they have been very non-critical.

This would be the same requirement for a SEPP OTL circuit.

I've actually built amps with no filters in the output section power supply at all (they hummed of course but a lot less than I expected); from the sound of your post I am thinking there was some sort of error in your circuit. My guess is it has something to do with the way the regulated supplies were set up.

My 2 laboratory CRC Schumberger regulated power supply (100-400VDC@250mA) were set up floating, as required. A third psu was used for the driver circuit. The driver was the one used in my SEPP OTL (for 4x6080WA). Something was probably wrong somewhere... May be it required much more drive than the SEPP as it only cathode loaded ?

I've run dead shorts on the output of the amp with the amp at heavy clipping (I do this as a demo at shows), pulled tubes out while the amp was playing music (I do that at shows a lot too), stuff like that and the amp acts as if nothing is going on at all. The circuit, IOW is unconditionally stable- stable with any load and any input condition. I doubt any SEPP would stand up to that...

No doubt : the SEPP withstands tube removals, output short-circuits or open (no load) outputs - and I only heavy clip my Fenders !

I have built my SEPP OTL in 1993 and work since then, and are able to give 20Wrms@8ohms with 4x6080, with a 5Hz to 60KHz bandpass @ -1dB @ 20Wrms, with a switchable lo FB (0 / -6dB) to match different kind of speakers. I would have been pleased to have equivalent results with my circlotron trials : unfortunately, I had idle instabilities instead, 7-8Wrms power@8ohms and the bandpass @-1dB was 5Hz to 25KHz. Indeed, something was wrong somewhere...

A+!

 

[cnpope]

Lol if they can read English: I'll slip 50 pesos into your pocket! Little persuasion.



I'm in the middle of nowwhere: Uruguay. Internet shipping for iron would cost a fortune and then customs fees and bribes. In the end I'd be able to buy a ticket to the UK and bring one back myself.

Just power EI transformers here.

2 secondaries: ilimzn didn't like that idea! Lol. I thought 2 secondaries would be sufficient for floating supplies. I'll do some more reading.



Thxs. good to know. I'll get some custom quotes versus surplus step downs.

I meant two 117V secondaries on each transformer; hence a total of four totally independent HT supplies; two for each channel. The key point is two independent secondary windings per channel. Whether they are on one transformer or two is unimportant.

I didn't realise you are in Uruguay; I made the mistake of thinking from your username and the flag that you were in the UK!

Chris

 

[Brit01]

Using a fixed bias to drive the grids on a 6080 am I looking at a 30-40 negative voltage requirement on each rail if the plate voltage is around 100-120 volts?

I have 6080 cathode resistors of 3.9R. I should be getting about 0.35 volts across them to achieve about 90 mA right after adjusting the negative grid bias with the fixed bias on the CF drivers?

 

[Brit01]

Success.

At exactly -40 grid voltage at 101 volts on the floating supplies, 3.9R on the cathodes I measured just 35mV DC on the outputs.

(just 1 channel to test with 2 x 6080)

Should I be getting this figure lower??

Does my LTP need to be more balanced? I'm using a SV83 as a CCS as the tail.

Maybe a SS CCS will balance them a bit more?



I know on my SS amp I have about 12-15mV.