Schaub Kongress H (1950)

[AlanBeckett]

Thermister?

Alan

[Geaney]

Yes indeed, thermistor - I've ordered up a few CL90's - should arrive today or tomorrow.

Cheers, John

[Geaney]

Thermistor made no difference. I guess it's not too surprising on reflection. The device limits current but there's no current flowing until the valves start conducting.

Since the overshoot is well within tolerance I think I'll leave it at this stage unless you guys have other ideas I could try........

Cheers, John

[pwdrive]

The high HT at switch on shouldn't be a problem for the valves John, just make sure any HT related capacitors are rated enough, you could leave the thermistor in circuit as it will limit the surge current through the rectifier and res/filter caps at switch on, you can always add a series R if the working HT is too high with the new silicon rectifier fitted.

The preferred thermistor for rectifier surge limiting in the old radios used to be the Brimistor CZ10:

http://electrojumble.org.uk/DATA/STC_Bri..._Types.pdf

Lawrence.

[Geaney]

Thanks Lawrence, I think I'm OK in terms of being well within spec of the valves and the filter caps, etc. so I'll leave it for now. I've put a series resistor after the rectifier diode and when things settle down the B+ is just below the spec so I'd say it's good for now anyway. I used one of those 15W resistors in a metal housing that is bolted to the chassis for good thermal transfer so it runs much cooler than the previous version. I'll have to see about getting some of those Brimistors!
Cheers, John

[Geaney]

The Schaub is back playing away again after however many years. There was no proper way to secure the mains cable so I rigged up a small bracket which will be reasonably invisible once the back is fitted. I mounted the dropper for the B+ on the chassis and added a dollop of heatsink compound for good measure.

The finish is not perfect so I might re-do it later on. It came up really well after a thorough clean and polish so I'll leave it for now.

An interesting project for me as I learned a lot about working with series string sets. As always a big thanks to everyone for all the help along the way

Cheers, John

[Mark Hennessy]

The cabinet does look very good in the pictures. It's an interesting set - especially with the "phantom FM". Could it be a deliberate omission for UK versions, perhaps?

Incidentally, I have the same JBL loudspeakers in my workshop! Sadly, one of mine has rotten foam surrounds, so buzzes somewhat. I'm trying to decide if it'll be worth fixing them with the repair kits available on eBay...

Is that an Agilent DMM you have?

[Geaney]

Yes, Agilent model U1273AX.

I doubt this set was sold in UK. I got it from a lady who lives in Ulm in Germany. The set belonged to her parents. I've seen photos with the FM module fitted so either it was an option or the set itself was released before the module was readily available.

Cheers, John