Advance H1E ECC88 Variant Schematic

[Electronpusher0]

This follows on from this thread:
https://www.vintage-radio.net/forum/...ad.php?t=59984

I too have recently acquired an Advance H1E LF Oscillator. Vicboduk was kind enough to e-mail the manual for the H1E, however it seems that Advance changed the valve lineup since that copy of the manual but retained the model number!
The version in the manual uses V1: 6SN7GT, V2: 6SN7GT, V3: 6X5GT and mine uses 2X ECC88 and an EZ80.
However the circuit is 90% the same. Principal changes include
Obviously valve pin number changes
Moving the thermistor from V1 Anode to HT via a capacitor to V1 Anode to 0V via a capacitor and fixed resistor
Change to the cathode circuit of V2a and the way the signal is fed from V1.

I have modified the schematic to reflect the actual circuit of the ECC88 version and added measured voltages, I attach it below in case it is of use to others.

Peter

[factory]

Thanks for adding that version.

I'm now wondering when they stopped making these, as mine has capacitors dating from 1974 & newer resistors than the one in the linked thread. Also looks to have ceramic tags strips similar to those found in Tek test gear.

David

[Electronpusher0]

Mine has the ceramic tag strips also and these seem to be original.
Mine matches the image in the linked thread (although I have changed the dogbone resistors as they had drifted significantly in value).
In your photo there is a hole in the chassis directly under the two right hand electrolytics, on mine there is a chassis mounted, three tag electrolytic comprising 2X 16uF and an 8uF occupying that hole, on my schematic I have indicated the colour of the tag alongside these components.
I am also going to change the two 13Meg resistors in the oscillator section (mounted on the range switch) as one of them has dropped to below 11Meg, they are supposed to be 1% components). I have found a source of 1% high value resistors but have to make 13M from a 6.8M, 2X 2.2M and a 1.8M all in series.

Peter

[ronbryan]

How about 8.2M and 4.7M in series?

Ron

[Electronpusher0]

The highest value I could get at 1% was 6.8M unfortunately.
Peter

[factory]

Originally Posted by Electronpusher0

In your photo there is a hole in the chassis directly under the two right hand electrolytics, on mine there is a chassis mounted, three tag electrolytic comprising 2X 16uF and an 8uF occupying that hole
Peter

All the date codes I can see in mine are similar, it came from a local (closed) repair shop that was being renovated around 8 years ago and despite being quite rusty/corroded I was surprised it still worked.

I also noticed two extra chassis holes next to the valve sockets, could an earlier build have had all the electrolytic capacitors chassis mounted?

David

[Electronpusher0]

I also noticed two extra chassis holes next to the valve sockets, could an earlier build have had all the electrolytic capacitors chassis mounted?

The extra hole to the right of the pot, between the pot and V1 & below V2 in your first photo is also present in mine and the one in the linked thread.
This has two small holes either side and is the right size for another pot.
In the previous (6SN7GT) variant there is another pot, R11, 5K Dubilier in the Cathode circuit of V1a, this has been replaced by a fixed resistor of 1K8 in the ECC88 version, I wonder if the early ECC88 versions also had a pot in this position and this was changed to a fixed value later in the production leaving the hole vacant.

Peter

[Electronpusher0]

I received the high value 1% resistors today and assembled the chain to make 13Meg, checked them on my DMM, reset my brain when I realised I was testing it on my anti-static mat, no wonder it read low....
Anyway, I replaced the two 13M resistors in the lowest frequency range and tested it.
The upper 2 ranges were fine but the lowest had heavy beat products with 50Hz. When set to 40Hz the output looked like an 80% AM modulated one.
Then I realised that I was testing without the screening can over the tuned circuit, when the can was refitted the 50Hz went completely. It seems that it was the stray field from the mains transformer. Two brain resets in one repair, I need a beer.

Peter