Do beware of the filter capacitors. These are a trap. The number of times I see hassles here is amazing.

The spkr field of 661 is in the CT of the Transformer B (-) Not B+. Be very careful and make sure that both capacitors have their positives on the HT [cathode of the rectifier]. If not they will be a short.

That will drag the HT down disasterously.

Marc

Whilst it maybe late in the piece: I have forwarded Brad a copy of the boards from the 661 I overhauled.

This may be clearer than those of the diagram as these are of one with the same Philips EBF2G mod made mid 1941.

These I actually drew from the boards; It is converted to pdf from AutoCAD.

NB: The information I have notes that there is an issue with the choke (spkr field) failing. There is a note on the pdf as this one's field failed.

Note this is in the Earthing or CT lead not B+. Both positives go to B+ one grounds and the other goes to CT. I mounted these between two tag strips on the edge near the 6V6 (not faraday cage).

By standing the resistors off, this way they get better cooling and the caps can be mounted with the resistors, keeping it all neat.

Marc

One of these HMV 661 units has been dumped on my bench by a mate & the circuit as posted above was most helpful in sorting a few things out but the quality/resolution of the images are not the best & really test my eyes.
Is there available a better quality copy of the circuit & this particular one had been modified to use a EBF2G which appear to be no longer available & someone has gone to great lengths to make up an octal base with a 6N8 in its base sitting on the top and a very neat TC connection sitting at the side.
It appears to be working OK as I have quite healthy audio from the volume control on but the RF stage looks rather dead with a weird 70V -ve bias on the grid of the 6J8G where I was expecting to see around 8V as derived by the R20 R2? voltage divider. The -ve 75V I think is driving the front end into cut off & preventing it from functioning. It has gotten to the stage where I have shoved it to one side on my bench whilst I do other things & every now & then I have another shot at it.
The electro dynamic speaker was tossed by my mate as the cone was U/S & I have substituted a 1800 ohm 50W WW resistor to replace that & dragged an old Rola 12" per mag speaker out of my bits & pieces to replace the missing one & mocked up a 6 pin plug to replace the missing one by breaking up an old 57 valve to get a 6 pin base.
Most of the HT voltages are around correct but as to be expected with no choke action from the field coil I do have some hum which is not insurmountable.
I intend to replace the 6N8 with a 6B8G which I have once I get the beast working to some degree.

Any better circuit copy around for this model??
Lindsay

The circuit appears in AORSM's but I will probably still have a scan. Many of the scans of these circuits are ordinary, but if that is how the source material is, the only way to fix it is to redraw it & that's a hell of a lot of work.

One common issue with any newly refitted radio is that the interference with it often causes it to be "deaf" the only way to fix that is to calibrate the set. Most manufacturers always tell you to re-calibrate the IF, if you have changed parts in the RF section.

I will attempt to calibrate the set first after refit, after that the minor annoyances can be sorted, or spotted. I calibrate using an oscilloscope as the measuring instrument: Amazing what it often shows (that cause more work).

Marc

(redundant)

You could try replacing the EBF2G with EBF35 or 6AR7GT.

with a weird 70V -ve bias on the grid of the 6J8G where I was expecting to see around 8V as derived by the R20 R2? voltage divider.

I think you mean the R1 and R2 voltage divider? +70 volts on the screen grid is ok, although +90 volts would be closer to the original design.

Robbert,

The R numerals are very much a guessing game on the copy of the circuit that I have & it is the 2 resistors around pins 2 & 3 of the speaker socket which divide down the volt drop across what should normally be the field coil. It then heads off towards another resistor which I think is R12 below the 2nd IF & then across to the aerial coil set which ends up on the top cap (G1) and there I see 70V -ve which makes me smell a rat somewhere.
R1 & R2 as best I can make out are part of the B+ feed to 6J8G screen grid.

It looks like the cap from the anode of 6K7GT may have broken down but that point is a +Ve voltage??

Got some spare time at the moment so will fire up the soldering iron & start lifting leads off to try & track it down.

GTC..Will Unhide my email as requested.

Thanks all, Lindsay

That's a strange situation. According to the diagram, the junction of R1 and R2 goes to 6J8G Pin 4 and not to the tuning gang.

The junction of R5 and R12 (I think it is) should have a slight negative voltage and is what goes to the aerial coil, then the tuning gang and then the top cap of the 6J8G.

Anyway a summary of approximate expected voltages on the 6J8G pins:
3 - DC = 200-250, AC = results of mixing process
4 - DC = 90 or so, AC = 0
5 - DC = slightly -ve, AC = local osc signal
6 - DC = 90 or so, AC = strong local osc signal
8 - grounded
TC - DC = slightly -ve, AC = antenna signal
1 - not used (should be grounded)
2 & 7 = heater supply

Anyway, good luck with finding it.


EDIT: I see you edited your post while I was working on this.. the cap on the 6K7 anode should be about 100pf, if you think it's faulty it can be disconnected temporarily. I'm mystified why an AGC line would go to the speaker, you could temporarily disconnect R12 if you think a rogue voltage is coming from there.

Obbert,

Yes I did Edit my post as when I did some more checking I realised that you & I were talking about 2 entirely different sets of resistors. The AGC line has no connection to the speaker circuitry but the -ve bias starts there with what I am sure are R20 & 21. The CT from the HT does not go to earth as usual but heads off to the field coil & R20 & 21 sit across that lead to earth tapping down the 100 or so volts there that are -ve due to the field coil. The CT lead goes to pin 2 of the speaker socket & R20 &21 are then wired to earth at the Extn Speaker terminal & the centre of those 2 resistors heads off to R12 (approx 8-10V -ve). They just used those socket pins as convenient terminating points.
There is something really screwy around the 6J8G & the 6K7 & around the tag strips associated with those valves... I have already removed 3 long solder slivers stuck in odd spots...a sloppy soldering operator at the plant I think as no sign of any other subsequent soldering in those areas. Solder slivers & wire off cuts create absolute mayhem in circuits & I once had a valve amp from a drive in cinema shut down due to a piece of wire off cut jammed into the socket of one of the output valves shorting to pins together = dead amp with weird voltages. It was one fine strand of 10/10 hook up wire which was almost impossible to see.

Thanks for the voltage info around the 6J8...in this case the TC is way high -ve...like 70V??

Lindsay

Can you try switching between MW and SW a few times? Those switches can go intermittently open circuit. Is the antenna coil on both bands conductive? (not open circuit). If you measure the voltage starting at the TC and working back to the AGC line, where does it change?

Do remember that the circuit for the modified one with the Philips valve is not the same as the other one. Measuring with a some digital meters with RF present may be unwise, unless it's paperwork says it can be used where there is RF.

They used analogue meters so digital will read high.

Voltage on the plate is a tad high 20% variance is considered normal; 6J8 should have about 236V on the plate. High voltage can result from new, not leaking caps. Otherwise its lack of conduction, some thing is perhaps not working.

That set is back biased, there should be a voltage of around 13V between the chassis & centre tap if all is working (chassis positive).

Well some progress on getting the set to come to life.

First up the rather weird higher than normal voltage readings I was getting was due to two things...the meter I was using was 100K ohm per volt sensitivity & was picking up signal from the 6K7 which was oscillating madly. I swapped to using a 1000 ohm per volt meter & things looked a lot more normal as far as voltages went although I am seeing a higher HT voltage due in part to the fact that I am only using a 1800 ohm 50W resistor in place of the missing field coil.
The entire set seemed lively enough up until the 6J8 as that valve appeared dead as a dodo but checked OK in the valve tester. Aerial coils all checked OK for DC path & the oscillator was going well after changing a couple of leaky paper caps. The CRO showed that the oscillator was tracking OK as the tuning gang was moved across the band. But the RF side of the 6J8 was not playing ball at all.
Went probing around with the CRO lead & around the first IF transf found a weird looking waveshape that sort of had the oscillator signal superimposed upon it.
Shorted the osc grid to ground & there was still a steady wild looking signal on the grid of the 6K7. This 6K7 I bought is metal shell type & comes out on pin 1 & that pin on the socket had no connection.
Whacked an earth on there & the weird looking wave shape vanished & the set showed some life, tuned around the band & could pickup all local Perth AM stations albeit very noisy with a lot of hash & absolutely NO control over the volume.
So now looking at the replacement tube for the EBF2G which I think Robbert advised me could be replaced with a 6AR7GT & appears to be working OK.

The mods that were done to use the EBF2G appear to be correct but by the time I blow the drawing available on this site up big enough to print out & see are VERY fuzzy.

Is there any chance that you Marc could email me a copy of that modification...my Email address is "unhidden"...it would greatly assist.

Lindsay

GTC..Will Unhide my email as requested.

I thought my offer may have been redundant given that the schematic images were already here, however I have now emailed them to you as PDFs.

GTC,
Offer not redundant at all as what came through via Email prints up better/clearer than what I could download from this site which are a great help but the fine detail on resistor/capacitor numbers was very hazy whatever way I attempted to print up.

The emailed copies are vastly finer detail & have made this chase a lot less of a drama.

Thanks, Lindsay

Success it now works well after many wild goose chases!!

The 6AR7GT appears to be way too sensitive as a direct replacement for the EBF2G with virtually NO control over the volume even with the TC disconnected audio was still getting through via the diodes in the tube. Lifting the leads from those killed the bleed through audio & by just moving the wiring slightly closer to the pins the audio was again coming through.

Rather than rejig the entire socket & many resistors to go back to the original 6B8G in desperation I put the 6N8 cobbled together valve & sockets unit somebody else had made back in and bingo full audio control with plenty of volume.

So if anyone else needs to replace an EBF2G (which are now almost impossible to source) one can get a 6N8 to work beautifully in place of the EBF2G by mounting the 9 pin 6N8 socket on top of an salvaged octal socket & mocking up a TC outrigger connection to suit that lead.

If I can work out how to post a pic of the 6N8 socket mod I will do so. Looks weird but it works well.

Hopefully the owner will be happy to just have it working & not be overly fussed that there is a weird valve arrangement in the back. If he really wants it "original" I guess I am up for some fun reworking the old EBF2G socket to take the 6B8G & getting it all to work as well as it is now.

Thanks for those that helped with circuit & advice.

Lindsay