Roberts R66

[Refugee]

From BangGood the slightly more "posh" AN8008 can be had for just under £15. I bought two so that I can have one in each place where I am likely to need a meter. They sure are priced to sell.
For measuring vintage selenium rectifiers you do still need an AVO 8 or 9 with a good 15 volt battery. I have a 9 for that.

[Terry]

I appreciate the suggestion when replacing resistors to start high and work lower until a correct value is found but I do not have access to a stock of components and would have to buy from a remote supplier with postage charges higher than the value of a small number of components.

There are at least two solutions here.

One is to make a list of all the values you are likely to need and, assuming that you are going to continue restoring more sets, possibly add a few others to give you a small stock. Some sellers used to sell several resistors in each popular value in a package at quite reasonable prices, I don't know if they still do. You'll be spending more money at the outset but with only one postage charge.

Another possibility is to cast around for local shops and engineers who still repair sets - they are few and far between, but still exist. They will need full ranges of a wide variety of components and I'm sure will be only too happy to sell you some!

Have you looked around to see if there is an Amateur Radio Club anywhere near you? You may not be interested in the amateur radio side of this hobby but they will also be using many of the same components that you will want.

Here are some links I've collected over the years. I haven't checked them all out and I can't vouch for any of them but you may find them useful.

http://www.auctiva.com/stores/viewstore2...id=1699714&page=home
http://www.partridgeelectronics.co.uk/index.htm
http://www.squirestools.com/electronic-components.htm
https://www.bowood-electronics.co.uk/index.php
http://www.allcomponentsltd.co.uk/electr...nents.html
https://www.componentshop.co.uk/
https://www.bitsbox.co.uk/
https://www.donberg.co.uk/catalogue/
https://www.ebay.co.uk/str/jpgelectronicschesterfield

[LyntonP]

From BangGood the slightly more "posh" AN8008 can be had for just under £15. I bought two so that I can have one in each place where I am likely to need a meter. They sure are priced to sell.
For measuring vintage selenium rectifiers you do still need an AVO 8 or 9 with a good 15 volt battery. I have a 9 for that.

I have ordered one of these meters and look forward to using it in future projects.
I also appreciate the list of suppliers which I will study at some length. I have only used one supplier up to now and have always had great service. I am not really experienced enough to say what components I am likely to need but I have been ordering slightly more than I do need for current projects in order to build up a small stock and even now I’m  seeing recurring components used in different radios. I have made some progress with the AVO battery and I hope to have this finished tomorrow. What I do need is some new leads for the AVO so there is another item for the next order.
Thanks again for all the advice it is much appreciated.
Cheers
Lynton

[LyntonP]

More work on the Roberts today. Changed the LT selenium rectifier for two diodes and brought the mains voltage up slowly using a variac whilst monitoring the LT. Ended up with a couple of resistors in series to achieve a LT of 1.39 volts. I now know the total amount of resistance I need so the plan is replace R15 and 16 in order to achieve the correct voltage. I will have to order some low value resistors. Domestic duties over the next few days but I hope to make a battery for the AVO over the weekend.
Again thanks for all the help
Lynton

[Refugee]

I made my AVO 15 volt batteries from five 3 volt CR2032 coin cells stacked with a 15mm water pipe stop end with a bit of tape wound around to hold it together.

[Terry]

From BangGood the slightly more "posh" AN8008 can be had for just under £15.

This is the meter with the capacitance ranges that Lynton wants that I linked to in my previous post, on special offer - £13.25 until 28th February - then back up to £18.62.

[Refugee]

I got mine for £13.something too.

[Terry]

Ended up with a couple of resistors in series to achieve a LT of 1.39 volts.

I'd aim for lower than that. Did you read the thread by Michael Watterson that I gave you a link to?

Conclusion

Above 1.2V performance is fine. Above 1.35 life is short. Life is x2 at 1.25 and life is 1/2 at 1.43V

Do whatever Philips/Mullard say!

Remember that these valves were designed to be used with zinc-chloride cells (alkaline weren't around in those days!) Although sold as 1.5V cells, nothing could be further from the truth. A fresh cell can easily be much higher than this but, on load, the voltage drops fairly rapidly until it reaches 1.4V, at which it remains for a while before starting off on the inevitable long slope to extinction.

Now, we don't know anything about the condition of the valves you have, other than they work fine, so might I suggest the following experiment? Monitor the filament voltage whilst slowly turning the Variac down until you reach the point where the performance starts to deteriorate, or stops altogether. (I am aware that the HT will also drop while you are doing this but it shouldn't be sufficient to cause any problems.)

Having determined what this low point is, endeavour to achieve a filament voltage approximately half way between this level and 1.35V. This should ensure the maximum valve life as well as good performance.

By the way, did you find the missing 25mA?

[Terry]

I made my AVO 15 volt batteries from five 3 volt CR2032 coin cells stacked with a 15mm water pipe stop end with a bit of tape wound around to hold it together.

You must start a new thread to discuss your mystical properties!

In the meantime, pray tell how you get 20mm diameter cells to fit into a hole designed to take a 15mm pipe.

[pwdrive]

I made my AVO 15 volt batteries from five 3 volt CR2032 coin cells stacked with a 15mm water pipe stop end with a bit of tape wound around to hold it together.

You must start a new thread to discuss your mystical properties!

In the meantime, pray tell how you get 20mm diameter cells to fit into a hole designed to take a 15mm pipe.

You need to look at the component parts of a compression fitting 15mm stop end....

Lawrence.