Pilot Little Maestro pre war AC/DC 1939 restoration project.

[ms660]

Looks about right if heat sinked properly:

https://www.ohmite.com/assets/docs/acl_hs1.pdf?r=false

Lawrence.

[Radio Scotland]

Originally Posted by ms660

Looks about right if heat sinked properly:

https://www.ohmite.com/assets/docs/acl_hs1.pdf?r=false

Lawrence.

Cheers lawrence, Just a lot smaller than i was expecting it to be.


Jay

[ms660]

No problem, my other half used to work for ARCOL at Threemilestone back in the early 1970's.

Lawrence.

[Radio Scotland]

Originally Posted by ms660

No problem, my other half used to work for ARCOL at Threemilestone back in the early 1970's.

Lawrence.

Free resistors ?

Chassis has been cleaned up, Still waiting on the dropper parts.

[agardiner]

Nice job on the chassis.

[Radio Scotland]

Originally Posted by agardiner

Nice job on the chassis.

Cheers, Cheapo cleaner from the quid shop


Well iv'e made a start and changed the smoothing caps and audio coupling cap. Not keen on the way iv'e routed the coupling cap wire to the valve base

And yea smoothing caps are cheapo china jobs but close to their stated value although the ESR Is a tad high, Old ones have lower ESR But quite a way from their marked values. But thats not too critical in this application. Even a lot of apparently good quality caps these days are fake anyhow.

Wee bit of chassis J-Hooking going on too, But my iron ain't big enough for direct to chassis work.

[Sideband]

Those old ones aren't original anyway. They look like Radiospares (RS) 1960's types.

[Radio Scotland]

Originally Posted by Sideband

Those old ones aren't original anyway. They look like Radiospares (RS) 1960's types.

Yeah, Pity the original canned one is gone but frees up space

[agardiner]

Originally Posted by Radio Scotland

Yeah, Pity the original canned one is gone but frees up space

I generally use that space for fitting the dropper.

[poppydog]

Originally Posted by ms660

No problem, my other half used to work for ARCOL at Threemilestone back in the early 1970's.

Lawrence.

Where were arcol in threemilestone back in the 70s?
I would have PMd you the question but you don't seem to be accepting messages, not from me anyway.

poppydog

[Radio Scotland]

Originally Posted by agardiner

I generally use that space for fitting the dropper.

Theres a spare pin on the rectifier gonna use that as a mounting point for the dropper, Vacant can space for HT Resistor and heatsink


Jay

[ms660]

Originally Posted by poppydog

Where were arcol in threemilestone back in the 70s?
I would have PMd you the question but you don't seem to be accepting messages, not from me anyway.

poppydog

I think more or less in the same area where they are now but the unit might have been smaller back then, it was called the Ashburton Resistance Co. Ltd back then.

I don't do PM's anymore.

Lawrence.

[Simon Gittins]

That's 10W when bolted to the chassis (heatsink), it will be less if it's not; however, it only needs to be more than 2W so that will be fine.

HT resistor calculations:

L14 resistance 650Ω
L14 voltage drop 202 – 160 = 42V
HT current 42/650 = 0.065A

Heater current = 0.3A

Originally, the total current through the 115Ω section of the line cord between mains and rectifier anode was 0.365A so voltage drop was 0.365 x 115 = 42V (so about 200V at rectifier anode).

A 470Ω resistor passing just the HT current will have a voltage drop of 0.065 x 470 = 31V (which is close enough). The power dissipated is 0.065 squared x 470 = 2W

[Radio Scotland]

Originally Posted by Simon Gittins

That's 10W when bolted to the chassis (heatsink), it will be less if it's not; however, it only needs to be more than 2W so that will be fine.

HT resistor calculations:

L14 resistance 650Ω
L14 voltage drop 202 – 160 = 42V
HT current 42/650 = 0.065A

Heater current = 0.3A

Originally, the total current through the 115Ω section of the line cord between mains and rectifier anode was 0.365A so voltage drop was 0.365 x 115 = 42V (so about 200V at rectifier anode).

A 470Ω resistor passing just the HT current will have a voltage drop of 0.065 x 470 = 31V (which is close enough). The power dissipated is 0.065 squared x 470 = 2W

Some good info there simon, So i'll be about 10v high on the rectifier with a 470 ohm resistor ?



Jay

[ms660]

The power dissipated by the rectifiers surge limiter resistor will be greater than that calculated using the DC load current figure for I in the Isquared*R formula for power dissipation.

Lawrence.

[Radio Scotland]

Originally Posted by ms660

The power dissipated by the rectifiers surge limiter resistor will be greater than that calculated using the DC load current figure for I in the Isquared*R formula for power dissipation.

Lawrence.

Over my head i'm afraid lawrence

[Radio Scotland]

Ok i'm hoping to get the dropper wired up soon,. Thinking of using some spare tie points on the 25Z4 Rectifier to mount the dropper parts, Ideally pin 6 to heater, Is pin 6 internally connected to the valve ?

[ms660]

Originally Posted by Radio Scotland

Over my head i'm afraid lawrence

It maybe but it's a fact, in the rectifier circuit in question the power dissipated by the surge limiter resistor will be much higher than that calculated using the load current figure.

Here's a quick reference to that...2nd sheet then the first few lines in the 2nd paragraph:

http://www.r-type.org/pdfs/uy41.pdf

It applies to other valve rectifiers as well.

Lawrence.

[ms660]

Originally Posted by Radio Scotland

Ok i'm hoping to get the dropper wired up soon,. Thinking of using some spare tie points on the 25Z4 Rectifier to mount the dropper parts, Ideally pin 6 to heater, Is pin 6 internally connected to the valve ?

Pin 6 = NP = No Pin which normally means no pin 6 is fitted to the valve base.

Lawrence.

[Radio Scotland]

Originally Posted by ms660

Pin 6 = NP which normally means no pin 6 is fitted to the valve base.

Lawrence.

Well it is fitted on mine, Get what your saying now about the limiter power,



Jay