New Pre amp thingy

[Richard]

Originally Posted by bob orbell

Colin, the WD PSU III, is designed to provide about 5mA to phono and about 15mA to the pre, your new pre thingy, is obviously consuming more, you will need to reduce the value of R4, if you have taken the supply from pre output, the PSU will supply about 50mA. Instead of loosing power to resistors, regulated power supply's are supreme, that is why I have gone that route. Bob

Hi Bob, Col,

If I've calc'd it correctly, PSU3 should be fine for HT current,

Phono2/3 consumes 4.3mA and Pre3 consumes 23mA

The new pre consumes 10.6mA

PSU is set for 250V as standard so Col may need to add line resistance for 180V.

[Richard]

Originally Posted by bob orbell

Colin, another problem may be the two Russian 6H1 tubes, I think these consume a lot more current both HT and heater, (double the heater current of a 6DJ8) 6DJ8 / 6922 would been much less power consuming. Bob

Using 1x 12AU7 (300mA) and 2x 6H1 (2x 600mA) heaters will be the same at 1500mA 6.3V
as the 5 valves in Phono + Pre3 (5x 300mA)
so all in all it looks a good fit.


I've just seen Col's PSU is only putting out 206V and is already down at 174V so not sure if there's extra resistance or some other reason in the line.

[colin.hepburn]

Originally Posted by Richard

Using 1x 12AU7 (300mA) and 2x 6H1 (2x 600mA) heaters will be the same at 1500mA 6.3V
as the 5 valves in Phono + Pre3 (5x 300mA)
so all in all it looks a good fit.


I've just seen Col's PSU is only putting out 206V and is already down at 174V so not sure if there's extra resistance or some other reason in the line.

Colin
Hi Bob/Richard
You have both just posted on the same things I was thinking about last night.
First to update you on the PSU3 it was built as per the old PSU2 meaning it has all four caps on the PCB with the 200volt Zenner diode fitted that’s giving me the 206volts on the pre out HT.plus 260v phono with no load

There is a 1k resistor plus 100uf cap in the WAD CF case so ht is around 198 volts ish under load

However I have noted that the Zenner and R4 22k 2 watt gets much hotter than it did in the old PSU2 as does The LM1084 running Bobs old WAD CF conversion pre. And the older Phono2
OK to the new pre thingy

Yes running it on the PSU3s Pre-out HT.206v
Note thought just to avoid confusion that I posted two schematics of the same new pre thingy the first sch the one I built for 240 volts which has the drawing error on the HT line

The second cleaner looking sch runs at 180v the only difference between them is R8 3K9 2watt for the 240v ht the one I have built and 2K2 for the 180 volts HT. So I could run it off the PSUs 250v out.

I was running the new pre on the 206v output thinking the 250v is the phono that’s when realised I hadn’t taken into account the heater current of six valves as that would be in the region of 2.700mA well over the TX current

so if I stay with the now renamed New Pre thingy, I will have to build a second. PSU to run both the pre and phono so would do same as Bob and regulated the power supply's

[bob orbell]

If you are building another PSU Colin, I have two transformers, two chokes and two good used PSU-III PCB,s one half populated, if interested, drop me a PM, ditto if any other member wants the other. Bob

[colin.hepburn]

Bob you have PM
Colin

[bob orbell]

Originally Posted by bob orbell

If you are building another PSU Colin, I have two transformers, two chokes and two good used PSU-III PCB,s one half populated, if interested, drop me a PM, ditto if any other member wants the other. Bob

Thank you for the interest chaps, all now gone to the first two askers, Colin and Dave. Bob