Amp initial testing.

[pre65]

Hi-thanks for the support

Now i am progressing to the PT15 filament supply.

In order to test,and adjust the 6v supply i measured the filament resistance at 1.3 ohms,so i inserted a 1R5 wirewound as the load (near enough ?) and it seems that with a 1R sense resistor the maximum voltage i can get is 5V !!

Would changing the sense resistor give me that 1 more volt ?

UPDATE.i was going to cancel this post but having had another thought,and trying an actual PT15 connecting the filament pins with them there clip leads i now get a steady 6V with the 1K pot roughly in the centre position.

MAGIC.-


The regulator does not seem to be over hot,so my heat sink must be doing its job.

[pre65]

Hi-me again !

Now testing the C3g DC heater supply,which is as the one in the WD forum FAQ section.

With the 1R5 resistor the voltage was to high so i chopped it out and clip leaded a spare 1K pot in its place to get 6.3V and,allowing for probe resistance it reads 6 ohms.

Now that is not a standard value.

As i have no proper load on the transformer at the moment (using one 6.3v winding) would that change in loaded conditions ?

Or should i just use AC heating for that one valve using my special cat 5 twisted twins cables !

[andrew Ivimey]

Well so far so good then.

Philip, you said that the PT15 filaments didn't glow red when you tried them a while ago. Is this still the case? This prob. isn't a prob.

And I wonder if Dave would confirm that his 6B4G filaments don't glow when working like my Svetlanas. The valves do warm up and get toasty anyway!

Onwards!

[pre65]

Hi-i see Bluebell list a 6R8 9W wirewound !

I've adjusted the pot to 6.8 ohms and i get a gnats firkin under 6.3v.

Problem solved ?

[Nick]

First, don't use the cold resistance of the fill as any indication of anything, use Ohm's law to work out what resistor to use to test the supply.

If the PT15 expects 6.3v at 1.5A (can't remember if thats right), then the resistance of the fill must be (when hot) 6.3/1.5 = 4R2, so the 1.3 is far to low.

If you thimk about what you have done, tyrying to get 6.3v across a 1R5 resistor will require 6.3/1.5 = 4.2A a bit more than the supply is designed for.

Finally, don't expect DHT fills to glow like indirectly heated valves, unless they are thorated, they will be a very dull red.

[Dave the bass]

And I wonder if Dave would confirm that his 6B4G filaments don't glow when working like my Svetlanas. The valves do warm up and get toasty anyway!

Onwards!

Sorry for delay in replying, been out the workshop for a while.

Nope, the 6B4G filaments only just light up with 6.3V DC on them. That took me by surprise until Nick explained about thorated bits and pieces, they don't run as hot.

DTB

[pre65]

Hi-just been talking to Phil Ramsey (Bluebell),what a VERY nice man he is.

He has offered to post my two resistors straight away and (wait for it) at no cost to myself (ie FOC)

I hope you dont mind Nick but i had a chat with him about forums and he seemed interested that you had started this one so i will give him the address.

[Andrew]

Are we talking about the C3g or PT15 fils?

confused.

-- Andrew

[pre65]

Hi Andrew- BOTH !

The last few posts have been about the C3g 6.3V DC supply,using the WD FAQ circuit fed from the 6.3v winding on the main transformer.
The circuit shows a 1R5 resistor but by chopping this out and using a spare 1K pot adjusted to get 6.3V i have found that a 6R8 resistor should do the job.Thats what i have got coming.

The PT15 DC supply is 6V using a circuit Nick posted on WD some time ago using a 9V toroid,scottkie bridge and an LM317T in current mode with a 1R sense resistor and 1K pot.

Time for lunchtime nosheroonis now !

[Dave the bass]

I've found that you wouldn't know the C3g's are alive unless the lights are off as their metal can blocks out most of the glow, only around the base can you see a faint glow on mine (speaking of which Philip, I've can give you your loan C3g back as my quad from Germany have finally arrived, VMT for that.) The OA2's have a lovely purple glow at the base which looks very pretty!

6B4G's glow a little, you can just make out the heater/cathode element in a 'V' shape peering from the top of the valve.

DTB

EDIT. Wots the 'prettiest' valve when it's lit, natch I'd need to make an amp with them in next seeing as DHTski's a bit of a minger

[pre65]

Hi-you could start with mercury vapour rectifiers !!

[andrew Ivimey]

If you can see the glow in a C3g, our Andrew ... well you are a clever chap

and those little 0A2s do glow a bit, eh! I must find a use ...

Dave, My 6B4G Sylvanias and Ken Rads glow so they must be Thoriated. Svetlanas don't.

So Philip R, might join the BB. I am sure he would be careful not to be commercial. And I'd very much enjoy his company. If you speak to him, Nick, be stern but if at all possible, welcoming.

[Nick]

I hope you dont mind Nick but i had a chat with him about forums and he seemed interested that you had started this one so i will give him the address.

Of course not, I keep meaning to phone hime up some time, its been a long while since I have a long natter with him. The last time I spoke I was at work, so there was only so much wittering about triodes that my fellow workers could be expecetd to stand

[pre65]

Hi-well everything seemed ok so i soldered in the HT connection for the valves,then switched on.I had made up a dummy load for the speakers.(2 off 15ohm power resistors parallelled=8 ohm)

No smells,pops,bangs or crackles but the bulb lit up !

Wiggling the PT15 put the bulb out (bad contact on pins ?)and all seemed well.

Time for action.Using my old Aiwa CD player and a passive pre and hooking up my experimental OB speaker i was puzzled,even with max volume no hiss,or buzzing of any sort.

Time to put a CD in,press play,turn up the volume-Well stuff me-IT WORKS !


I am so relieved,just hope no 2 (the black one) works.

[andrew Ivimey]

Excellent!

onwards!