12-07-2020, 08:28 PM
(This post was last modified: 12-07-2020, 08:29 PM by Mike Watterson.)
Dansette Consort, approximately 1963. There are maybe two later versions using the same BSR deck. I think Currys also used the same deck.
Not really looking for help, though I managed to lose one of the domed grey feet in the workshop.
1) Opened up and noted using PCB and Philips "mustards" which I think are Mylar (=Polyester, PET approximately). No more trouble than most modern met-polys.
2) Replaced selenium rectifier. I know they can be OK, but not concerned with originality under the chassis on something 1960s I might pass on. I'm not keeping it. I put 82 Ohms >3W approx in series.
3) FF & RW didn't really work. Found all the grease had set. Circlips on two arms and both reel holders. One circlip went Boing! Found an identical replacement, eventually.
4) No record. Actually nothing on erase head. Checked solder joints, wiring, osc coil, R/P switch etc. Nothing found. Checked resistors around the EL84 (Amp on play, Osc on record). Swapped ECC83, just because. One resistor seemed madly off. Whipped it out and it was 24K rather than 22K, which should be OK, NORMALLY.
5) Left it running. Bias and Erase appeared, but I thought a low level. Indeed now loud sounds recorded, but no erase.
Maybe time to look at the service info / schematic? Looked up RMorg to discover it's been in my attic for a LONG time. It's in my collection there.
Also no mic. But I decided to try a cheap Ross Electret on the basis that maybe the original "crystal" mic had a high output and I could add a one transistor amp. However it was able to close the ! DM70 magic eye at 7, talking normally. DM70/DM71 seem to last forever if the filament is OK.
I found it curious. It says later versions the R13 is a pot instead of fixed 750 Ohms. The pot seems to only affect bias in Dub mode. Mine has the pot. But ALSO later versions have a 6.8k Ohms in PARALLEL with the R16, 22K. Why do that rather than a 5.6K, or just a 6.8K? My 6.8K resistors look either stupidly tiny or about x3 bigger. So I thought I'd try 2x 15k in parallel, soldered to the track side of the PCB across R16, 22K. There was then massive erase AC on the erase head. Used tape totally silent and recordings listened to by two 3rd parties were said to be perfect, "Better than my walkman", said one. I said that wouldn't be hard.
I didn't check C13 to see if 150pF (original) or 1500 pF (alleged later) as the tone control seems fine. The R&TVS isn't always 100% accurate. I could believe R16 being reduced in value (sets oscillator gain), but not later production models having a 22k and 6k8 in parallel. I guess with slight EL84 ageing or lower HT (our Irish mains is 10V to 15V less than England) you'd need more feedback. 22K is the top of a potential divider with R17, can't read it on schematic, maybe 56k?. Anyway, 7.5K in parallel with the R16 22K is fine.
The replacement Electret mic seems OK and recording from the speaker of a decent VHF-FM set was fine.
The filament bias for the DM70 seems curious; it looks like one side is fed from a centre tap on the heater supply connected to 0V/Chassis via 25 uF electrolytic and 8k2 in parallel with it. The other side of the filament to the 6.3V AC via 82 ohms. The DM70 grid connects via a 470K & 2.2M to 0V to the v1b (ECC83) anode. The DM70 anode HT via 1M from main HT is disconnected on Play.
Now to find the missing foot and re-home it!
There are only three models of tape machine I'd keep:
1) A German battery valve portable tape recorder with spring drive for the tape, like a windup.
2) The early Sony transistor portable reel to reel that uses a spring drive for the tape.
3) The portable Sony Elcaset machine. Looks like a professional portable reel to reel, but uses the 1/4" tape cassettes.
The Compact Cassette was originally intended to be a dictation machine, but the quality was gradually improved. I was given a Teac with belts that turned to goo. I have replacement belts, but I lost interest while cleaning the goo and considering the exploded drawings. Anyone want a box of all the bits and new belts?
I gave away a Sony TC77 reel to reel and I'm wondering who to foist a 1950s BBC/EMI behemoth that is curiously described as "portable". Maybe if you have two GAA or Rugby players to cart it and a very long extension cable. Not restored but seems in good order.
Not really looking for help, though I managed to lose one of the domed grey feet in the workshop.
1) Opened up and noted using PCB and Philips "mustards" which I think are Mylar (=Polyester, PET approximately). No more trouble than most modern met-polys.
2) Replaced selenium rectifier. I know they can be OK, but not concerned with originality under the chassis on something 1960s I might pass on. I'm not keeping it. I put 82 Ohms >3W approx in series.
3) FF & RW didn't really work. Found all the grease had set. Circlips on two arms and both reel holders. One circlip went Boing! Found an identical replacement, eventually.
4) No record. Actually nothing on erase head. Checked solder joints, wiring, osc coil, R/P switch etc. Nothing found. Checked resistors around the EL84 (Amp on play, Osc on record). Swapped ECC83, just because. One resistor seemed madly off. Whipped it out and it was 24K rather than 22K, which should be OK, NORMALLY.
5) Left it running. Bias and Erase appeared, but I thought a low level. Indeed now loud sounds recorded, but no erase.
Maybe time to look at the service info / schematic? Looked up RMorg to discover it's been in my attic for a LONG time. It's in my collection there.
Also no mic. But I decided to try a cheap Ross Electret on the basis that maybe the original "crystal" mic had a high output and I could add a one transistor amp. However it was able to close the ! DM70 magic eye at 7, talking normally. DM70/DM71 seem to last forever if the filament is OK.
I found it curious. It says later versions the R13 is a pot instead of fixed 750 Ohms. The pot seems to only affect bias in Dub mode. Mine has the pot. But ALSO later versions have a 6.8k Ohms in PARALLEL with the R16, 22K. Why do that rather than a 5.6K, or just a 6.8K? My 6.8K resistors look either stupidly tiny or about x3 bigger. So I thought I'd try 2x 15k in parallel, soldered to the track side of the PCB across R16, 22K. There was then massive erase AC on the erase head. Used tape totally silent and recordings listened to by two 3rd parties were said to be perfect, "Better than my walkman", said one. I said that wouldn't be hard.
I didn't check C13 to see if 150pF (original) or 1500 pF (alleged later) as the tone control seems fine. The R&TVS isn't always 100% accurate. I could believe R16 being reduced in value (sets oscillator gain), but not later production models having a 22k and 6k8 in parallel. I guess with slight EL84 ageing or lower HT (our Irish mains is 10V to 15V less than England) you'd need more feedback. 22K is the top of a potential divider with R17, can't read it on schematic, maybe 56k?. Anyway, 7.5K in parallel with the R16 22K is fine.
The replacement Electret mic seems OK and recording from the speaker of a decent VHF-FM set was fine.
The filament bias for the DM70 seems curious; it looks like one side is fed from a centre tap on the heater supply connected to 0V/Chassis via 25 uF electrolytic and 8k2 in parallel with it. The other side of the filament to the 6.3V AC via 82 ohms. The DM70 grid connects via a 470K & 2.2M to 0V to the v1b (ECC83) anode. The DM70 anode HT via 1M from main HT is disconnected on Play.
Now to find the missing foot and re-home it!
There are only three models of tape machine I'd keep:
1) A German battery valve portable tape recorder with spring drive for the tape, like a windup.
2) The early Sony transistor portable reel to reel that uses a spring drive for the tape.
3) The portable Sony Elcaset machine. Looks like a professional portable reel to reel, but uses the 1/4" tape cassettes.
The Compact Cassette was originally intended to be a dictation machine, but the quality was gradually improved. I was given a Teac with belts that turned to goo. I have replacement belts, but I lost interest while cleaning the goo and considering the exploded drawings. Anyone want a box of all the bits and new belts?
I gave away a Sony TC77 reel to reel and I'm wondering who to foist a 1950s BBC/EMI behemoth that is curiously described as "portable". Maybe if you have two GAA or Rugby players to cart it and a very long extension cable. Not restored but seems in good order.
