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Old 20th April 2015, 12:12 PM   #1
shrad is offline shrad  Belgium
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Default Faylon P200 rebuild

hi all,

I'm not reading this place often but I have to go grab a Faylon P200 today which is in a used untested condition but was never opened and saw good storage conditions (from the seller's point of view)

this is a double EL503 push-pull which seems nice enough for decent guitar/bass abuse, or even a nice subwoofer amp...

can anyone give any information on this amp? I know this is a bargain considering the price of even a chassis and its side components so if the tubes are dead I'll buy it anyway

please see the schematic to have a better idea

Click the image to open in full size.

I plan on a proper cleaning, rewiring and parts replacement but if anyone has better suggestions (other than put EL34s in it obviously )
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Old 20th April 2015, 07:18 PM   #2
shrad is offline shrad  Belgium
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got the beast, not so bad condition but has clearly been opened before

I'll post pictures later if needed

one EL503 has a tiny blob of molten metal => flashover if I guess it right...

anyway for 60€ it's still a bargain

can somebody point me to the right direction on how to test the circuit for proper voltages/currents without damaging the amplifier?

for what I recall, paired tubes are not required for dual tubes but I may be wrong... does bias pose problems in that case?

thanks for anyone helping!
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Old 20th April 2015, 08:40 PM   #3
shrad is offline shrad  Belgium
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correction to my previous post, those are not dual tubes as I thought but single pentodes, so will need to be paired right?
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Old 21st April 2015, 09:05 AM   #4
shrad is offline shrad  Belgium
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after a bit of thinking, I was wondering if it would help if I duplicated the bias circuit for each tube so that I could use any replacement without caring much about matched pairs

that particular amp is known not to sound that good, would redesigning the B+ and bias supplies be a good idea?

other components seem to be in good state, I'll make sure to post pics tomorrow as I'm off from work
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Old 28th April 2015, 07:11 AM   #5
shrad is offline shrad  Belgium
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is it even worth posting a picture of the amplifier?

could anyone have some pointers?

I have sourced a spare EL503 from a friend online, but it is not paired and I don't know if those tubes or even that design is resilient regarding pairing

may I remove the extra tube from the damaged pair and readjust bias to have a single pair provide half the power?
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Old 29th April 2015, 03:40 AM   #6
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Looks like a similar amp to the Bogen MO100A:

Bogen beasts again

A minimal front end, into high gm outputs. Which are horribly expensive now. And known for unreliability.

Certainly, adding more bias adjusts is helpful. Using only a single set of tubes, you will want to connect 8 Ohm speakers to the 4 Ohm output taps.

I think I would consider converting the thing to some cheaper TV sweep tubes.
Maybe with "Schade" local feedbacks on the outputs, so the global N FDBK can be kept safely lower. A bit more gain up front needed then, so maybe use a small Mosfet Concertina phase splitter to save a tube socket.
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Old 29th April 2015, 07:51 AM   #7
shrad is offline shrad  Belgium
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I'd like to convert to other tubes like GU-50 or EL36 but then I'd need another PT for higher B+, or a doubler which is not a nice thing

my idea if I was to do a conversion would be to use a PFC controller as a B+ supply as it would have good characteristics and would not require a big PT

another concern is the OT, would I be able to keep it for higher impedance tubes?

I'll first try duplicating bias control for each tube and use that spare EL503, then for later on I may try converting it
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Old 29th April 2015, 05:20 PM   #8
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The reason I mentioned the TV sweep tubes was that you COULD run with the same B+ and OT. Most of the TV sweep tubes can handle higher current than the audio tubes. Usually the issue is filament current with them. But going to one output pair instead of two should keep that under control. 6HJ5 would be a good fit. Can get 100 Watts out with them readily. No plate cap. 6.3 V filament. About $5 each. Excellent curves in Schade mode. (Schade and g2 drive curves attached, and pentode and "triode" curves too.) George (Tubelab) used these on Pete Millett's DCPP red board (Schaded outputs) with good results. Takes two 6CB6 drivers (7 pin), or could go to 6JC6 (9 pin) drivers. The Schade curves on these are better than a 300B. You'll need around +150V for the screen grids.

http://frank.pocnet.net/sheets/084/6/6HJ5.pdf

Posted new P-P power amp design

The GU-50 will require a higher B+ and a new OT.

The PFC controller modules I have seen do not have isolation from input to output. You could run one through an isolation Xfmr I guess.
Attached Images
File Type: jpg rsz_6hj5_s.jpg (35.6 KB, 31 views)
File Type: jpg rsz_6hj5_g2.jpg (56.2 KB, 29 views)
File Type: jpg rsz_6hj5_p.jpg (50.6 KB, 27 views)
File Type: jpg rsz_6hj5_t.jpg (36.4 KB, 28 views)

Last edited by smoking-amp; 29th April 2015 at 05:49 PM.
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Old 29th April 2015, 08:31 PM   #9
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You need to measure the primary impedance of that output transformer (OT). If that's really a 200 Watt amp, the primary Z could be rather low. If Zpri is less than 2500 Ohm, you may have to use something more robust for a (single pair) TV sweep output tube, like a 35LR6 or 26HU5.
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Old 29th April 2015, 09:31 PM   #10
shrad is offline shrad  Belgium
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thanks a lot guys, I'll have a go at a complete dismantle friday and will post pics

the transformer is massive and will be measured as I can
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