It is time: The Fisher TA-600 - Printable Version
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RE: It is time: The Fisher TA-600 - morzh - 04-17-2017
Yellow are made, amongst others, by Kemet, Illinois, Cornell-Dubilier - all major quality mfrs.
RE: It is time: The Fisher TA-600 - Mondial - 04-18-2017
As Greg said, one of the output tubes is gassy or has grid emission. It goes into a thermal runaway condition where as it gets hotter, the plate current increases which makes it hotter.....
The Russian tubes are also probably run over their ratings, as the 7189 has a higher plate voltage rating than the EL84
The problem is compounded by the fact that there is a common cathode bias supply for all four tubes. If one tube draws excessive current, the negative bias only increases by only 1/4 the amount as if there were individual bias resistors.
RE: It is time: The Fisher TA-600 - Ron Ramirez - 04-18-2017
I've just learned that the 6П14П-EB has higher ratings than the 6П14П. I wish I had known that before I bought the used 6П14П tubes...
So I suspect the 6П14П is more equivalent to EL84, and the 6П14П-EB is more like the 7189.
Well, I do have a set of four 6П14П-EB tubes on the way...they finally made it from Ukraine to New York so I hope to have them by the end of the week.
RE: It is time: The Fisher TA-600 - Ron Ramirez - 04-19-2017
More parts have arrived!
[Image: http://www.philcoradio.com/images/phorum/TA600/ta600_023.jpg]
Digi-Key doesn't fool around when it comes to ordering parts. I ordered them on my lunch hour Monday; less then an hour later I received notification that they were shipping my order. Two days later, here they are. Usually when I order from Mouser, they don't fill the order until the evening after I place the order. Their shipping is just as fast, once they ship the parts.
Anyway...
Wow, those 1/4 watt trimmers are tiny! Having never built an IBAM board before, I did not know how big the board should be...now I see I could have bought a board about 1/2 the size of what I purchased (2" x 2").
The next big question...where the heck do I place this board, and what do I do to hold the board in place? The "where" seems pretty obvious...as close to the output tubes as possible...but the "how to hold it in place" I find sort of puzzling at present.
RE: It is time: The Fisher TA-600 - gregb - 04-19-2017
Digi-key truly amazes me with their shipping speed, I can place an order at 8:00pm and its on my door step at noon the next day. Not sure where it ships from for Canadian orders but that truly does amaze me and the worst case is it only costs $8 and better yet is free when you buy more than $200.
Gregb
RE: It is time: The Fisher TA-600 - Ron Ramirez - 04-20-2017
Thief River Falls, Minnesota isn't all that far from the Canadian border, but they are just under 1000 miles away from you. And they are just over 1000 miles from me. I use $8.99 FedEx Ground shipping; I avoid USPS whenever possible.
Hmmm...I wonder if they do ship from a Canadian location for your orders? Next day shipping from that far away, and across a national border, is pretty amazing
RE: It is time: The Fisher TA-600 - Ron Ramirez - 04-20-2017
From Ukraine...four NOS-NIB 6П14П-EB tubes have arrived.
[Image: http://www.philcoradio.com/images/phorum/TA600/ta600_024.jpg]
[Image: http://www.philcoradio.com/images/phorum/TA600/ta600_025.jpg]
As morzh had mentioned in a previous post in this thread, you can see the diamond with a number inside, indicative (per morzh) of Soviet military tubes, below:
[Image: http://www.philcoradio.com/images/phorum/TA600/ta600_026.jpg]
Notice how clean those tube pins are.
These tubes are the ones I will be using in the TA-600 when it is complete. But first...I still have quite a bit of work to do to this receiver.
RE: It is time: The Fisher TA-600 - gregb - 04-20-2017
Yup, those are the ones. You will be happy with them Ron, they work well and sound nice. I have been using them for a few years now with my own stuff as well as customer gear and no complaints and so far not a single failure.
Gregb
RE: It is time: The Fisher TA-600 - morzh - 04-20-2017
BTW, the tubes you've gotten are from Saratov tube factory "Reflector".
My birthplace. I mean the city
RE: It is time: The Fisher TA-600 - Arran - 04-20-2017
(04-18-2017, 12:12 AM)Mondial Wrote: The problem is compounded by the fact that there is a common cathode bias supply for all four tubes. If one tube draws excessive current, the negative bias only increases by only 1/4 the amount as if there were individual bias resistors.
That does not sound like a very good circuit design for cathode biasing, it's more typical to see a common cathode resistor and capacitor combo for each pair of tubes rather then a quartet of tubes. As for gassy tubes, I've seen this with a #224 tube I bought over fleabay, the tube tested fantastic for emission, which I immediately knew was wrong thanks to the blue glow. If the 6П14П that was red plating was also glowing blue that would explain a lot, whomever sold it to Ron probably thought it was a new testing used tube and never performed a gas test.
Regards
Arran
RE: It is time: The Fisher TA-600 - Arran - 04-20-2017
(04-20-2017, 10:01 PM)morzh Wrote: BTW, the tubes you've gotten are from Saratov tube factory "Reflector".
They are still very much in business, although they changed the name apparently, that's where the Sovtek branded tubes are made, as well as the fake Svetlana tubes that New Sensor was pedaling in the U.S market.
Regards
Arran
RE: It is time: The Fisher TA-600 - Ron Ramirez - 04-21-2017
New Sensor is behind not only Svetlana, but also Sovtek, Tung-Sol (the new ones, not the old), new Genalex Gold Lion, and Electro-Harmonix.
https://newsensor.com/TubeSpecification.aspx
RE: It is time: The Fisher TA-600 - Ron Ramirez - 04-21-2017
Oh, Arran - the red plating 6П14П never had any blue glow. It was running in excess of its specs. It was as if I had plugged in a set of EL84s instead of 7189s.
Now I know the details.
6П14П = EL84/6BQ5
6П14П-EB = 7189, EL84M - higher ratings
RE: It is time: The Fisher TA-600 - morzh - 04-21-2017
Mike Mathews is an interesting personality.
The attempt of hostile takeover of his Saratov facility is the testament to how it is to work in Russia.
RE: It is time: The Fisher TA-600 - Mondial - 04-21-2017
Hey Ron, how does the individual bias mod work? Are you connecting individual trimmer controls in series with each of the output tube cathodes?
As I recall, the cathode bias for all four tubes is developed across the filaments of the 12AX7 preamp tubes. Since there is no separate negative bias supply, it seems the only way to individually control each tubes bias is to insert a variable resistance in each output tube cathode.
Edit: I just looked at the schematic and it appears that the full voltage drop across the tube filaments (23.5V) is not used for bias. There is a voltage divider of R158-R159 which sets the bias on the output tube grids to about -12.5V. It then would be possible to have individual voltage divider pots for setting the bias for each output tube.