Leland47
Super Member
How about a pic of yours Gadget?
Can you identify this tube amplifier?
- Thread starter sardox
- Start date
How about a pic of yours Gadget?
Its not mine. It belongs to Leesonic, its just living at my place for the moment until we figure out what to do with it. The 2.5 ohm output transformers make it not real useful in it's current form. The power transformer has been replaced and it would actually operate properly if I changed the caps.
http://audiokarma.org/forums/index....tube-amp-and-speakers-id.691289/#post-9237013
Its been cleaned up since then, and the power transformer and voltage doubler caps changed, along with new diodes, a power switch and a fuse holder installed. I got that far before I thought that maybe it would be smart to find out what the output transformers were. It basically stalled at that point. Probably should have done that earlier TBH. The 7189's are currently living in my Fisher 600, and I've probably used them for 3 hours. They test nearly dead, but it does the proper power output and they bias up OK. I'm calling BS on my tester because these work by every practical test I can give them.
http://audiokarma.org/forums/index....tube-amp-and-speakers-id.691289/#post-9237013
Its been cleaned up since then, and the power transformer and voltage doubler caps changed, along with new diodes, a power switch and a fuse holder installed. I got that far before I thought that maybe it would be smart to find out what the output transformers were. It basically stalled at that point. Probably should have done that earlier TBH. The 7189's are currently living in my Fisher 600, and I've probably used them for 3 hours. They test nearly dead, but it does the proper power output and they bias up OK. I'm calling BS on my tester because these work by every practical test I can give them.
Sorry I haven't replied, guys. I've been busy as heck with my wife and daughter...
Leland, I bought the amp without tubes. As per the matter of the 12AX7 vs 12AU7,
the guy I bought it from took the tubes and sold them, but he confirmed that there
were 12AX7 and 7189 tubes in there originally. If they were Mullards, I hope he
got top dollar for those... I'm going to bring a 24VAC transformer home tonight
to test out those output transformers. I'll hook it up to the outside primary leads
and see what kind of voltage I get out of the speaker outputs and attempt to
do the math. I'll post the results as I get them and maybe you guys can make
sense of it all
I'm hoping these are 4Ohm or more, Gadget. Let you know
what I find. As per the 7189 tubes, I doubt the plate and screen voltages
warrant such a rare/expensive tube. I assume I'll be able to use some decent
6BQ5/EL84 tubes without frying them, what do you guys think?
Leland, I bought the amp without tubes. As per the matter of the 12AX7 vs 12AU7,
the guy I bought it from took the tubes and sold them, but he confirmed that there
were 12AX7 and 7189 tubes in there originally. If they were Mullards, I hope he
got top dollar for those... I'm going to bring a 24VAC transformer home tonight
to test out those output transformers. I'll hook it up to the outside primary leads
and see what kind of voltage I get out of the speaker outputs and attempt to
do the math. I'll post the results as I get them and maybe you guys can make
sense of it all
I'm hoping these are 4Ohm or more, Gadget. Let you knowwhat I find. As per the 7189 tubes, I doubt the plate and screen voltages
warrant such a rare/expensive tube. I assume I'll be able to use some decent
6BQ5/EL84 tubes without frying them, what do you guys think?
Ok, I found a "24VAC" transformer at work and brought it home to test those OPTs!
Voltage into the primary (wires to the EL84 sockets) was at 29.32VAC. Tested the
voltage under load and without load, came out to same from testing transformer...
I left the B+ connection soldered to the capacitor. I hope I don't have to unsolder it
to test properly...
Voltage out of the secondary was .616VAC. Both OPTs tested within .001V
Where does that put these 9496237 OPTS?
Voltage into the primary (wires to the EL84 sockets) was at 29.32VAC. Tested the
voltage under load and without load, came out to same from testing transformer...
I left the B+ connection soldered to the capacitor. I hope I don't have to unsolder it
to test properly...
Voltage out of the secondary was .616VAC. Both OPTs tested within .001V
Where does that put these 9496237 OPTS?
Ok, doing the math per Gadget's suggestion,
I get a ratio of 47.5975:1.
If I square that, I get 2265.52.
If I use this amp with 4 Ohm speakers, that puts the primary at 9062 Ohms line impedance.
If the sweet spot for EL84 P-P is at 8000, then 8000/2265.52 = 3.53 Ohms for the optimal speaker impedance.
Amiright?
I get a ratio of 47.5975:1.
If I square that, I get 2265.52.
If I use this amp with 4 Ohm speakers, that puts the primary at 9062 Ohms line impedance.
If the sweet spot for EL84 P-P is at 8000, then 8000/2265.52 = 3.53 Ohms for the optimal speaker impedance.
Amiright?
Hey guys!
I finally got a variac and brought the amp up slowly...
Took about 6 hours to get from 10V to 80V, then left it at 80V overnight, and eased it up to 120V in another 4 hours.
The results are fantastic, this amp is dead quiet. I can't hear a thing at idle with a constant impedance source.
With 87dBWM speakers, I'm getting around 103dB of music output on average, peaks of 106.
Sound is very, very clean. Bass and mids are extremely clear and precise. Highs are accurate, but not
too harsh. The sound quality is, dare I say, better than my Magnavox 9302. Output power is much lower
than the Maggie, but I would imagine that the NFB circuit has a lot to do with that...
Thanks again to all of you guys for your help getting this enigma amplifier up and running!
Todd
I finally got a variac and brought the amp up slowly...
Took about 6 hours to get from 10V to 80V, then left it at 80V overnight, and eased it up to 120V in another 4 hours.
The results are fantastic, this amp is dead quiet. I can't hear a thing at idle with a constant impedance source.
With 87dBWM speakers, I'm getting around 103dB of music output on average, peaks of 106.
Sound is very, very clean. Bass and mids are extremely clear and precise. Highs are accurate, but not
too harsh. The sound quality is, dare I say, better than my Magnavox 9302. Output power is much lower
than the Maggie, but I would imagine that the NFB circuit has a lot to do with that...
Thanks again to all of you guys for your help getting this enigma amplifier up and running!
Todd
cademan
Lunatic Member
FYI, you really don't have to wait so long to ramp up the voltage. You would notice any abnormal current draw within the first 5 minutes and any smoking item can be easily replaced and noticed within the first couple of seconds of power up. Just keep your eyes on it. 
This is just me but I have been doing this for over 40 years and have not once waited overnight for any amp to get up to voltage even if it hasn't been used in years. Like I said, this is just me!
This is just me but I have been doing this for over 40 years and have not once waited overnight for any amp to get up to voltage even if it hasn't been used in years. Like I said, this is just me!
century tek
Addicted Member
Most of the time if there is going to be any smoke, it's usually caused by a shorted filter capacitor and most of the time cannot be reformed. Loud hum at power up usually indicates an open not shorted filter capacitor. I just don't even try to reform them, I just replace them.
the amp that has the stone looking floor or whatever behind it, i own it, bought it off of eBay the tone crest logo on the wood may be it brand but could never find any info on it. I've seen many variations of this amp and i believe it is an amp built for many different consoles . the ultimate upside to it is that it came with the same sonotone tubes which are mullard blackburn rx1 tubes very nice. i could never find a schematic on it. only thing i can help with is the eia code on the paper taped to the bottom of the wood lit.352