Another Advance E2 Signal Generator.

[Electronpusher0]

Split from this thread:-

https://www.vintage-radio.net/forum/...d.php?t=156763

I have just won an auction on ebay for an E2 so my adventure with them is just beginning.
Apart from the usual checks on electrolytics what other components should I check.
Mention is made of using a cheap external frequency counter module to monitor frequency (post 7), presumably the full rf output is used for this purpose.

Peter

[g4aaw pete]

Originally Posted by Electronpusher0

Mention is made of using a cheap external frequency counter module to monitor frequency (post 7), presumably the full rf output is used for this purpose.

Peter

I think that would result in destroying the input circuitry of the counter.
I bought such a counter, about £8, and it's very sensitive.
I wound a piece of wire round the oscillator valve on my B40, and there was enough signal from this to drive the counter reliably.

[Electronpusher0]

I have just received the E2 and on opening it I see that it has been modified.
The transformer has either been modified or replaced. There is a label on it giving the connections for linking for 105 to 125 or 205 to 250 as per the schematic but someone has hand written on it 0, 230, 250. The mains is connected to 0 and 230
Additionally there is a secondary missing. according to the schematic the rectifier valve should have its own winding for the heater but instead the heater is in parallel with the other heaters with one end grounded.
The main electrolytics have been replaced by an RS dual capacitor and much increased in value, the first cap after the rectifier has been increased from 16 to 64u and the second capaciytor has increased from 16 to 100u
The series resistors have also been changed, the one from the rectifier cathode to the first capacitor has been REDUCED from 560 to 22 ohms and the resistor to the next cap has increased from 1K to 2K (2 X 1K in series).
Would these mods be considered safe, especially the increased capacitance for the rectifier?
According to the valve museum, "In normal use the maximum reservoir capacitor is limited to 4 µF and the minimum series resistance has to be 150 Ohms."

Peter

[WME_bill]

Advance E2.
The 6X5 rectifier is rated for operation with the other heater supplies, the heater cathode insulation rating allows 450V heater to cathode. So that is perfectly satisfactory.
The reservoir capacitance quoted by the valve makers (RCA) is 10uf, assuming a reasonable transformer winding resistance.
The limiting factor is the peak charging current. Here the valve is operating so very well within its maximum ratings that you don't need to worry.

The revised smoothing capacitors were maybe what was in the spares box when they were fitted. I get the impression that the previous owner was worried about hum, and so had an exceptionally smooth HT supply.
With a 64uf reservoir capacitor, a series resistor of 22 ohm sounds a bit low, unless the resistance of the transformer HT windings are higher than usual. If you are concerned, why not put back the 560ohm. The anode current is so low that it will hardly affect the HT rail voltage as the oscillator only operates anyway on 120 - 150v.
wme_bill

[Electronpusher0]

Thank you Bill, you have reassured me. It was sold as working, I have not powered it up yet. I will change the resistor back to 560 ohm as you suggest and power up slowly using a variac.

Peter

[Electronpusher0]

I have reformed the capacitors as a precaution and changed the 'orrible 'unts caps. The cathode resistor of the AF oscillator read 330 ohms instead of 3k3, I removed it and cleaned off the black residue on it and it went back up to few K so it also got changed as did a couple of high value resistors.
Bring up slowly on the variac and it now works well and surprisingly well in Cal.
I have changed the RF out socket to BNC and job done.
Very pleased.

Peter