Slightly OT: Any 5672 tube amp designs?

[ConanB]

So I have a bunch of these little 5672 tubes on their way, more than I really need for the FX pedals I'm going to try throwing them in, so I was thinking of other uses for them.

Anyone know if they can be used in any sort of mini-amp?
My electronics knowledge is still terribly lacking, so even any links for good tube related articles that could get me on track to designing up something myself would be even more useful at this stage 

I googled for 5672 related amps but couldn't find what I was after, but noticed an old AX84.com post by frequencycentral asking the same thing that didn't really get any more responses, so maybe there is nothing out there?

As always any info is greatly appreciated!

If I can't find any extra uses for them I'll probably end up with a few spares to trade off I guess 

Cheers,
Conan.

[frequencycentral]

I do have an idea for a push/pull amp using two 5672 and a 6111 submini dual triode, I've drawn up the schematic and done some tests, but I have no idea how to specify a suitable output transformer for it. My idea is to use a LT1054 to get the plate voltage up from a 12 volt supply.

I discussed the idea with forumite alextheian-alex, he said

"those tubes have a fairly high internal resistance, so they will need quite a drastic refelcted impedance stepup from the tranny to get where they will be the most efficient, but the data sheet seems to spec them around 20k, so I would start there."

"Best option is probably to get a Hammond 125E which has a zillion possible impedance taps.  It is always good to have one of those around for experimenting.  They cost $30, but are very useful for getting impedance load right without a ton of math.  They will be very big though."

That's as far as I've got.

I do have some 'other uses' for 5672 coming up too - did you see my 'Tube Stereo Panner' thread?

Rick

[frequencycentral]

Here's the idea so far:



I've fully tested the cathodyne phase inverter and the two pentode stages together - the outputs cancel each other, which is what is required for push/pull.

I'm assuming the first triode stage is fine too - it should be.

I haven't included the heater supply, from a 12 volt supply the 6111 heater would require a series resistor 19 ohm / 3 watt. The two 5672 would require a series resistor 100 ohm / 1 watt.

I haven't experimented with LT1054 yet, but have had good results using MAX1044 to achieve higher plate voltages. LT1054 would be more suitable.

So........it's part tested but slightly theoretical, until I (or you, or someone) hook it up to an O/T.

Fully open for hacking/tweaking/suggestions...............!!

[frequencycentral]

This thread has got me thinking. I've been doing some research and I think I've found a suitable transformer match to turn my Pentadriver into a little single ended amp. I think a Weber Reverb Driver (25K:8 impedance) W022921 / 125A20B would suit the 5672 pretty well. The load resistance of a 5672 is 20K so it's a reasonably close match. https://taweber.powweb.com/store/magnetic.htm

I can't find a UK supplier though - any ideas?

Pentadriver: http://www.diystompboxes.com/smfforum/index.php?topic=70533.0l

[ConanB]

I'm sitting at work so don't have the schems and stuff lying around, but doesn't the FireFly use a 22.5k/8k OT? Would that possibly be close enough? I did manage to find an AUS supplier for those, but thats not much help for you 

I got the 5672's to put together your FX designs which look great, and will probably get a few 6111's soon so I could definetely look into the SubAtomic. I might try and invest in that Hammond OT you mentioned.

And I like the idea of the PentaDriver as an amp since I'd love to have gain/tone/vol controls in any amp I throw together. I have a bunch of AX84 designs saved at home so I'm going to try and go over them to understand the basic "design" of a tube amp a little more.

Cheers for the responses!

[jonnyeye]

You could try a 140V line transformer with a 1W tap (this will be a 19.6K primary).  Edcor makes one (the WS4-140) for about $10 that would give you 19.6K:4/8, or you could use their WS4-100 100V line tx, use the 1W tap on the primary and hook up an 8 ohm speaker to the 4 ohm output tap (or 16 ohms on the 8 ohm tap) for 20K:8/16.  I haven't tried these, but Edcor has a good reputation.  They're also probably not air-gapped (maybe?), but the current (<5ma) probably won't cause too much core saturation... and if you needed a push-pull tranny, the 4W tap should work as a center tap.

If you try them, I'd like to know how it goes.

[SirElwood]

Fender reverb transformer (022921) has 15k primary and 8Ω secondary. That's close, and easy to get in europe.

This might be (and it is) a matter of opinion, but I would use these submin tubes for boosters and other fx-pedal stuff, and for a small "under 1Watt amp" my choise would be 6AU6 pentode. It needs a higher voltage (B+ 150V) but it's a "real amp". This http://www.ledsales.com.au/kits/nixie_supply.pdf would be a suitable power supply. And, it's easy to get 6.3 volts for filaments on that 9V transformer needed to run that step-up converter.

Just my 0.02€