Ultra Tiger Questions

[RobinBirch]

This will teach me to open magazines while I'm up to my eyeballs in other stuff.

I've got a radiogram that I bought years ago cos it looked nice. I knew that it was an Ultra but I didn't know what type and was going to find out "one day". Well I was skimming through the latest BVWS comic and came across a case restoration for an Ultra Tiger and went - That's my set!!!!

So, shift christmas cards of the top, look inside and sure enough it is a complete and, without taking anything apart on first glance, un-mucked about Ultra Tiger.

So I've pulled the valves and found that one has a total cathode short (MTP4 Output Pentode). My first question is theefore has anyone got one of these that could be sold/swapped?

Moving on, Looking at the set someone has been in there as the varios cap connections on the valves were disconnected and looking at the chassis there are two round holes.

Underneath the various bits are clean and there doesn't appear to have been too much mucking about but there is a two part electrolytic that doesn't look kosher which may explain the two holes in the top of the chassis.

Also everything appears to be covered in a fine layer of rust.

So, next question. I've never seen the insides of one of these before, should there be some big caps where the two holes are?

And following that. What's the easiest way of getting rid of the rust?

The photos show what I found. I haven't dismantled anything yet other than to pull the valves and have a brief look at the chasiss. It is all back together now awaiting some time to look at it properly.

Help

Robin

[Paul_RK]

Hi Robin,

Yes, the can under the chassis is probably replacing the two original big wet electrolytics. I was going to provide a photo of the chassis of my Tiger table model, but I hadn't been inside it for about fifteen years, and now that I look it's lost its original cans too. So here's a scan from Newnes Complete Wireless instead

Paul

[RobinBirch]

Hi,
That explains the two holes. As whoever did the replacement did such a reasonable job I'll leave it as it is unless I can come up with two equivalent cans and put them in place.

Now all I need is a new output pentode :-(

Robin

[PJL]

It should have been an AC/PEN. I presume you mean MPT4? anyway never seen a working example and I usually find an MKT4 in their place. Replacement MKT4's were made for a long time so there are still plenty about...I assume it's the 5 pin variety with side contact for the screen?

A heater-cathode short I guess?

I have just cleaned up a Marconi 296 chassis in similar condition using a rust remover. It's a messy job and requires coils to be stripped off. From what I can make out the very fine rust seems to be from the plating which unfortunately makes the remover less effective meaning a few coats will be required. The remover tends to lift good plating too.

[RobinBirch]

Ah ok, if an AC/PEN is what should be there then that is what I want, or something like it.

Yes, heater/cathode totally shorted, about 5 ohms.

What was the chassis plated with? It doesn't look like the residue that xinc leaves.

Robin

[PJL]

Whatever it was, it was applied to the tuning capacitor which made that appear rusty despite being brass underneath.

AC/PEN, MPT4 or most likely to work and be affordable is the MKT4 but make sure you get the appropriate base as these were availabe as B7 or B5 and side contact.

[Ian B]

I believe chassis were usually plated with cadmium, probably because it takes solder better than zinc (or so I read recently).

Ian blackbourn

[RobinBirch]

Ah,
If that is the case then this could be a little interesting. Firstly getting things cad plated is damn near impossible unless you have a friend in an aerospace/military manufacturer and secondly it is going to make cleaning it up a job for dustmasks rubber gloves and instantly laundried clothes.

Robin