Hello all.
I picked up the Empire State chassis from Tony H this afternoon I Left him the remains of the speaker in case he wants to send it for a rebuild. There is nothing left of the speaker apart from the frame , the rodents have eaten through the insulation on the field coil and eaten some of the windings as well. The speaker transformer has gone the same way. I think I will have no choice but to replace it with a 5 inch permanent magnet type. The problem will be finding somewhere to mount a choke . I am not sure if there is other components missing from the top of the chassis . I am going to ask Brad if he can down load some pics. It is not going to be an easy task making suitable brackets to mount a replacement speaker with speaker transformer and choke . Maybe I should just sit back in my chair and forget about it. Could you please advise if the top of the chassis looks complete if Brad can download my pics. Yes I did use a tripod and yes I used delayed trigger so hopefully they will not be blurred . I have ordered volume 9 from the HRSA I hope this will give me the drive and determination for this epic repair.
Kind Regards Jim

Jim since you are going permag you will need to drop the excess 50 or 100 volts that was allocated to the field coil across a resistor, say 1.5k 15 watts, assuming HT current of 100mA or less. This impedance will avoid the need for a choke, esp. if you increase the 2nd filter to say 16 or 22μF. The resistor could mount on the back of the square parts box tower or just about anywhere you can find space on the chassis:

https://au.element14.com/ohmite/hs151k5j/res-1k5-15w-solder-wirewound/dp/2946592?st=1500+ohms+15+watt+resistor

I may again have a suitable speaker and transformer, with bracket. I also have some silicone rubber wire which looks period and is heatproof. You'll need it, that resistor will get HOT. So mount it somewhere it can sink heat to the chassis.

Hello Ian.
Thank you for your advice. That will certainly save some space. I am not sure if there is bits missing from the chassis top. Have sent some pics to Brad.
Regards Jim

If you do go for resistance, which the circuit, or data sheet should tell you, current squared by resistance should give you an idea of the heat needed to be dissipated. I quite often use a panel mount type resistor, & RS components are one who has them.

That enables a side wall, or end to to be used as a heatsink. I normally bed the resistor on the heat transfer grease used for transistors & such.

At the risk of hum, dropping the value of the "B" input cap, or removing it (choke input filter) reduces voltage.

Marc

Thank you Marc.
I would think the hum would be quite significant. Both yourself and Ian have suggested using a dropping resistor . I do have a small choke in mind that I was hoping I could incorporate on a bracket around the speaker . I would need to check exactly what it is first,would this be better than the resistor if I can find a place for it? The power transformer only measured 25 ohms on the primary it seemed a bit low to me I would have thought it to be about double that. It meggers OK to ground. It is incredible the damage a rat can do . It may not have eaten the copper winding however it chewed through the insulation on the field coil and more than likely broke the winding with its teeth. I need to sort this part out before I bother with the rest. Ian you suggested silicon wire I would have a piece of 3 core silicon lead I cut off a crook appliance probably a sandwich toaster I could slice that up.
Regards Jim

I now know why this looks incomplete. Because it is, there is supposed to be an asbestos sheet alongside the 80 rectifier and a rectangular metal can along side it . That is all missing, what is supposed to be in the can, was it filter capacitors ? It is going to be quite a task to turn this sow's ear into a silk purse. I can feel me getting cold feet it is certainly a long term project.

Hi Jimb, just take it a problem at a time.
As usual would suggest getting it all going electrically and then look at the cosmetics.
Using a choke would be nicer and mounting on the speaker sounds like the go.
I'm not familiar with this model, the pix will be nice to see.
Fred.

I restored a Kriesler beehive in the late eighties using a metal clad ceramic resistor ratted from an old TV. It was mounted above the chassis to keep the heat as high up as possible. Only possible because this radio is totally enclosed in bakelite - wouldn't want such high voltage above the chassis if the back was open.
This radio was donated back to me by the owner having a cleanout as he is in his mid eighties now. Still works OK with quite acceptable hum, so a good solution until a choke comes along, and gets the power working so other issues can be sorted .

Thanks Fred and STC 830.
The cosmetics will only be an above chassis clean there is no way I am going to do a full strip down. Unfortunately it's originallity is lost anyway with a whole tin can missing .I think that may have contained oil filled, filter capacitors it has some other electro's roughly strung under the chassis . As you said Fred one problem at a time. I am feeling I was a bit brave taking it on. But it is not the first time I have felt that way. I am sure in the end it will work again.
Regards Jim

There are two principal filters. Where the rectifier valve is running close to its limit; We have the choke input filter, where there is no capacitor on the rectifier end. Then there is the capacitor input filter, where there is a capacitor on both ends. Designed properly, hum is not an issue.

Often there is a capacitor across a field coil. These are resonators forming a tuned circuit making it more efficient.

Depending on size & how you go about it a speaker transformer will fit inside the pan & that is done, especially when you have one with a live frame (PYE). The wet may have been tossed as leakage of the content, was often an issue. Some of us will have them. There are two large diameter ones under the radio bench here.

Marc

Thank you Marc.
I have found a choke which I think would be suitable it measures 519 ohms and 12.7 H. Will that be ok ?
The power transformer I think is ok. It measures 27.4 ohms and 21.8 mH. It again it seems low compared with others I have measured.
However it meggers ok to ground .
Regards Jim

Re the field coil and B+ current:

On the circuit for the Radiolette 29 and 71, the field coil is marked as 1600 ohms, but it's badly printed and could easily be read as 600 ohms.
However, the total HT current is listed as 45mA and the voltage across the Loudspeaker Field as 72 volts.

Et voila, 72/.045 = 1600! So 1600 ohms is correct!

So the 1500 ohm 15 watt resistor is well within its ratings, the actual dissipation is 3.24 watts. You could get away with a 5 watt resistor, although to reduce the surface temperature a 10 watt part would be better.

I suggest you keep C22 as 8 or 10μF 600v and make C23 47μF 600v. That will avoid the need for a choke.

Remember, you'll need the dropper resistor anyway, a choke will not drop anywhere near enough volts. In any case if you fitted a choke you'd need to keep it away from the speaker transformer to avoid hum.

I'm pretty sure I have a suitable speaker C/W mounting bracket for the speaker transformer.

Hello Ian, thank you for the information. I liked the look of that 1.5 k resistor I think I will order one it will bolt down somewhere with a good squirt of heat sink compound under it. Element 14 are such a Pain to deal with . Cannot see why they don't use PayPal.
Still trying to figure out a good way to mount a 5 inch speaker . I have a nice one however it is round and I will have to come up with a suitable bracket one with a squarish back section would have suited better. I have not come up with the circuit yet. I have ordered volume 9 from HRSA it is for these radios . I will have a circuit somewhere but at the moment I am just planning how to make a good job of the speaker mount. It was very inconsiderate of the rat not only eating the speaker cone but chewing the insulation off the field coil . It must have dug its teeth into the winding.
Regards Jim

Jim, Just sent an email to you with some good info on the Empire.
JJ

Thanks Johnny.
I have just printed it out.
Kind Regards Jim