• 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.

Breadboard 6C33C-B S.E.T

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Been doing some experiments with the 6c33c-b in SET mode on a bread-board-(nearly literally, Drawing pins make great soldering points!)

The layout is this,-

Two 7586, Nuvistors as SRPP input gain-stage, set at 10 mA, Stage supply 150V--( according to blurb this should be the operating point for class A--10mA@75V) capacitively coupled to the next.

Second gain/driver, is the venerable 6SN7, again in SRPP and set for 10mA, but Stage run at 300V capacitively coupled to the 6C33

The output stage, is the 6c33, set in Cathode Bias, running 200mA, stage supply set at 305V-( anode diss, at around 43 odd watts, dropping 86V accross cathode resistor, 430 ohm decoupled by 1000 mic cap) Im applying a small amount of neg feedback--Havent sat down and worked out how much, due to the next bit--.

The Output Transformer ---Hangs his head in shame, looks at shoes, and mumbles;) is a mains Tx, a toroidal, a 50VA, 240V to 25V from Antrim Transformers, type, C2016 both secondaries parralleled off. Ex Maplin Components. ( Not sure how far out this would be to to a proper Tx for the 6C33C-B--Any ideas??)

I think Im becoming a bit of a convert to the SET, as the sound considering the wrong type of o/p Tx is really rather good!--Even the other-half commented on the sound quality Guess I must be losing some power and range by using this Tx but it cant be that far out by its sound!--Havent done proper 'scope testing for power and response yet--Just never enough hours in the day.

Its amazing what you can knock up on a wet Sunday afternoon from the contents of the 'junk-box'!

Nearly finished the bread-board stage of the project, apart from adjustments when testing with 'scope etc. but have a question--Any idea what the maximum heater to cathode voltage is allowable for a Nuvistor? Doesnt say in any blurb I can find--Need to know as the upper of the two is at 75 odd volts and the bottom one is near zero--Ive set the heater potential at 160V, as the supply to the Nuvistor heaters also supplies the 6SN7, whose upper cathode is at 150 ish

Need to find a nice case and maybe even proper o/p Tx's to make stereo pair.

Alastair E At-- Murdering the SET Divn, SWC


Ill need to collect my sig-gen, which I lent out some years ago, but I need to get it and a couple of other things. Basic tests with 'Sound-check', indicate freq top end around 18K, but thats the top end freq on the disc--It was still level there. Lower response was hampered by the drive I was using (Dont Ask!)--now rectified so should be below 20Hz but needs checking!

How would you measure/calculate the impedance of say, the Tx Im using??--(never was good at the maths side!)
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