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hello
if you have a phono amp say a 2 stage ecc83 and between the stages the riaa filter
wich tube can you chance then without disturbing the riaa filter
i need lower gain from this amp and will chance one ecc83 to a ecc82 with the right bias ofcoarse
Follow Ups:
I would try a 12AY7/6072A as another poster suggests instead of a 12AU7. But you're up against driving that lossful network which requires GAIN. Definitely NO 12AU7, the B+ current draw goes way up with a 12AU7 and it will not drive that RIAA network. Ray
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
Ray
1) He has a 6072 in there now.
2) We are talking about the second tube
that doesn't drive the RIAA network.
3) He already stated that his PS
will handle the extra current.
4) The 12AU7 has alot more drive than the 6072.
DanL
Dan: 1. Forgive me but in my manual an ecc83 is the European/British designation of a 12ax7 not a 12aY7. 2. He clearly states he needs less gain and is pondering using a 12au7 instead of a 12ax7. 3. Yes, a 12au7 has more current drive not voltage drive than a 12ay7, it is a power amplifier not a voltage amplifier and a pitiful tube in my estimation when used as a voltage amp.
"The gift of imagination is a gift of the Gods imparted to a few who receive innumerable kicks in the a$$ their entire life." Le Corbusier (Charles-Édouard Jeanneret)
hello
It was a mistake from me i have indeed original 6072 tubes in the phono amp
and i have now the 12au7 installed as Dan told me
but i have the cathode cap still in place
the gain is good now
The sound is different i must play a few day now to get used to the sound
its a little fatter sound maby a little slower
then i will also try the ecc99
HornyTry removing the bypass cap.
It will only reduce the gain from 9 to 8.
I doubt you will hear the volume change.
You will hear the sound change though.DanL
PS What resistors did you use?
Wirewound will give you a fatter sound.
Edits: 03/22/12
hello Dan
i put some resistors parallel to the original resisters to get the values
i think these are carbon
the originals are tantalum
for any of the various " RCA phono style" circuits: grid resistance of either tube is assumed to be very high, so same general response...
you have to examine how the stages are set up, because you may find that the stages are cascaded with in the same tube, and you will need a twin triode with different triodes in same envelope (i.e. 12DW7 or equiv)...
Also generally, if you can just sub the tubes, I would try 12AY7 first, because it has lower gain: 40 vs. 100 for 12ax7, and it sounds better generally, with some versions sounding very good..., than a 12au7 wherein even the best versions sound only good...mmmm ( with usual correct bias changes for 12ay7, etc) ok???
Ok, thanks Good Luck to you,
-3db
hello -3 dB
this is the schematic the tubes are 6072
and i need lower gain and lower output imp.
Edits: 03/20/12
As yet anther option, you might consider replacing just the second stage 6072 with an ECC99. This will give you a much lower output impedance, even lower than 12AU7, which is a plus, as well as lower gain. However, the ECC99 will pull more current, as with a 12AU7. you would want to reduce the value of the plate resistor to about 22K to 33K, I think. As a final bonus, IMO, the ECC99 sounds better than 12AU7, most of the time.
hello Lew
that is also a very good advise!
I try both the 12au7 and then the ecc99
you say the plate resistor to 22 or 33k
but what value must the cathode resistor have then?
I generally would do this with the actual circuit in front of me, to make measurements, but you want more current for the ECC99 vs the 6072. Right now, you are getting a bit more than 1mA; you want 5-6 mA at minimum for the ECC99. So you could use a 200R cathode resistor, or something in that range. 200R in the cathode would give you 8mA, based on the data you have provided (1.6V divided by 200R = current). Then if you use a plate R in the 20K to 30K range, just check to be sure the ECC99 biases properly. For example, if you use a 22K plate resistor, you will drop 176V across it when the current is 8mA. That leaves ~80V plate voltage for the ECC99. Check the curves to be sure it will bias properly at 8mA and 80V. I think from memory that may be a stretch, if so maybe use a slightly higher value cathode resistor to drop current down a tad.
Horny
Use a 12AU7 with a 10K plate resistor and
a 150R cathode resistor-no bypass cap.
1/3 the rp and 1/3 the gain.
No bypass cap is a bonus.
You will be pulling more current though.
You had 1.33mA and you will pull about 11mA.
Make sure your PS is up to it.
DanL
Thanks Dan!
What do you think is the output imp? then with the 12AU7 tube?
the power supply is not a problem
and i gone try this tonight.I have one more question
the tube stage in front is this a sort srpp or something else?
and is this stage produce the whole gain of the tube or more?
Edits: 03/20/12
Horny
You're welcome.
The output imprdance is 4.8K.
Gain of 8.
DanL
and basically DanLoudAudioNut....has left me speechless...
I am assuming the last 6072 tube is in the same tube for both channels...you should verify this...
Otherwise, all I can do is confirm Dan's suggestions very good...
look on Tubes Asylum for the best 12Au7 variants and brands, etc.
I personally would use wirewound resistors in both Plate position, and cathode position, because they are quiet, smooth, sound great, and are available in the values Dan has suggested...
you probably don't want much more than the usual 3ft/1m cable...mmm
Have Fun, Good Music to you and let us know how is sounds
Sincerely,
-3db
hello -3dB
yes it is the same tube for both channels.
its a simple and quick to try
thanks
If the RIAA filter is passive then you can change the second stage and not disturb the filter except for the Miller capacitance of the second stage.
Chances are that won't make much difference.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Oke thanks Tre
so the riaa filter is made with influence of the first tube and the second is just amplification?
can i use every stage here?
"can i use every stage here?"I assume you mean "any stage"?
Yes, but if you use a tube with a lot of Miller capacitance you would get in trouble.
The 12au7 has less Miller than the 12ax7 so you will be OK.
BTW -3db's suggestion is a good one.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 03/20/12
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