abe:
the yamamoto is a 45 tube amp and it is tube rectified. i have a few 80 tubes that i can roll to see if that reduces the hum. i emailed kevin covi and he seems to believe the hum is caused by the 101D tube as when i switch the amp to mute, the hum disappears. I see! If that is the case, ask Kevin if the 101D's filament supply is AC or dc. If ac, maybe he can say if its possible to convert it to DC (by means of adding an SS rectifier inside the chassis). If that is the real source of the hum, using dc filament supply will knock down the hum at least 90 to 95%. IME! regards, Abe |
Hello Mark,
OT but, any news on the tubes?
regards,
Abe |
Hello Mark,
I responded to the your post in my system's page.
The trumpet is a good phono stage no question! The Chenin though is special. It has that liquid midrange but dynamics on the top and bottom are well balance. The Trumpet's bass is authoritative to say the least. this can be trace through the SS rectifier many irons used in the phono power supply design.
regards,
Abe |
Ping Stiltskin! Hello Mark, I forgot to add, my email account is arevz@msn.com Would you please drop me an email privately so I know where to reach you. regards, Abe |
OT: Ping Stiltskin!
Hello Mark,
I hope you received my email(sent weeks ago)to you regarding how wonderful the tubes I got from you are!
Thanks again!
regards,
Abe |
Hello,
First of, thanks Ait for sharing your findings. I appreciate the time you took to explain to us what you did.
After reading the post of using 7193 in place of the 6SN7's, I have a few quetions.
1.) Does the change in sound could be accounted for using a 7193 with the 6SN7 Operating Points? For example, if Mick is using around 240V at the plate (max for 6SN7 is 250V), then it means that the 7193 will now be bias soft (300V at the plate max) or quite in a conservative region. If so, will it be safe to assume that when you do this, you changed the original Supratek OP already and instead, what you have done is using the PSU of the Supratek to run 7193 tubes?
2.) Does anyone know if both triodes in each 6SN7's on the Chenin are being use as voltage gain stage or one as a CF (Cathode Follower ) only?
3.) Would it be too much if the original poster can post a clear pic of his preamp.
Apologies for my inquiries but I have an access to a 7193 preamp and I remember that the OP that sounds best in that specific circuit is around 275 to 280 volts on the plate with the Grid V around 8~9 volts. Just wondering and wanted to learn, that's all.
regards,
Abe |
Okay thanks! So it means that the triode in the 6SN7's are Directly coupled and both seems to be voltage gain stages.
No, I was not asking for changing the OP of the Chenin. Apologies if somewhat my statement sounded like that. All I am saying is, the preamp now run the 7193's using the Chenins 6SN7 designed PSU. So, it is possible that the change in sound is from variation of the operating voltages typical for a 7193 like changing its PD (Power Dissipation) due to different bias levels from that optimized or selected by Mick for the 6SN7.
Apologies again, I am not asking for a pics of the internals, just the outer layout. I just want to see what tubes were use in your Chenin since as far as I know, there are three versions (not sure but two I am pretty sure) of the preamps phono section and can be distinguish by what tubes being use in conjunction with the 6922's.
Thanks!
regards,
Abe |
Thanks Ait. Yes, our Chenin are different from each other then. Mine uses 6C4's. Great project you have there! That's a nice Tuner! I do not use my Chenin anymore. In fact it is on the sideline now. Maybe when the mood is right, then I will have the urged to listen to it again. Yes, I like the Chenin but like you put it, my Chenin is "so last week" also. Just kidding, I love the preamp and I am very happy that I invested my money on it. On my system page is the preamp I recently built. This is what I use nowadays. You can also see it on this link http://img177.imageshack.us/img177/1681/img4095gy6.jpgor http://members.myactv.net/~je2a3/friends.htm my system is at the very bottom of the page. Have fun tweaking then! regards, Abe |
Chelvam,
So Mick still take orders for preamps?
My officemate, after borrowing my preamp for a week, wants to buy it but I am not selling. If Mick still take orders, I can tell my friend to email him directly then.
regards,
Abe |
IMHO,
When the usual hit or miss tube swapping troubleshooting technique fails, you have to have a freq generator and a scope to solve problems like this. This is not just a matter of what "looks" broken anymore.
Your tech friend, how did he come up with the decision of replacing the resistor first?
Tell him to isolate the PSU circuit to the actual amplifier circuit. By feeeding very low freq signal at the input, you can tell if the power supply is the one with a problem looking at the modulation, if any, of the B+ signal. At mid to higher frequencies, you could test the real amp section stages by stages, assuming that the usual downstream B+ voltages checks out as it decrease when being decoupled from the stages, and see where the noise is coming from.
Please ask your tech about those. If he does not understand what you are talking about, find a different tech. It would be helpful also to plot the schematic first before poking around with the scope so that you can easily follow which point checks out in relation to the diagram.
Hope it helps...... |
ADDENDUM
My post above assumes that you already tried swapping amp, speakers etc. and the problem is in the linestage. If phono, and using a 6106 rectifier, I would take a look at the FET for that particular channel. The 6106 have a voltage drop of 60V, and a maximum dc current output of 125 ma. The 5AR4 on the otherhand is 17 and 250 mA. As you can see, the preamp is being starve not only with the voltage but also of the current when using a 6106. Since transistors are current driven, I would take a look at that first if it was me but using a 5AR4 rectifier.
I seem to remember that Mick was frustrated about units that was shipped back damage from using 6106 tube in the PSU before. IMO, it is possible that what i described above could be the reason.
I could be wrong of course ...... |
Hello Kgturner,
Me. I have not use my Chenin for almost 8 months now. Just sitting here, in saran wrap. You can see the preamp I am using in my system page.
regards
Abe |
What email address did you use to get hold of Mick?
Thanks in advance! |
Can anybody tell me if I could use a 5u4g in the rectifer postion, emailed Mick haven't gotten a reply yet.
Want to try the EML 5U4G mesh plate, looks like a very nice new production tube. Anybody try them? Snopro, Before you can use a 5U4G, you should know what rating does the filament transformer have in the PSU. The 5AR4 draws around 1.5 to 2 amps, the 5U4 draws 3 amps. It's been a while since I opened my PSU but if I remember it correctly, the rating is only about 2 amps. regards, Abe |
Thanks Kgturner!
I will let my officemate send his inquiries to that email address then.
regards,
Abe |
So, I tried the Mullard GZ33 tonight, and I like it a lot! I bought a pair, and both had good getter flashing, full lettering, and tested 100%+ on my tube tester (set to 5V4, 5U4 and 5AR4 settings). Compared to the GE 5AR4, the background is cleaner, the soundstage is more focused (I can tell more easily where the instruments are) and the bass is a bit tighter and deeper. Cymbals are cleaner and have more focus. I swapped the two tubes back and forth twice each (I didn't want to stress the preamp with too many rapid on/off cycles). It just sounded more powerful and focused with the GZ33 than the GE 5AR4 - I'm keeping it in. Hello, Good for you! I hope you are posting this as a result of your "own" experiment only and not for the others who have no time to understand what is going on in the circuit to try. With all due respect, are you saying that the preamp PSU (5V filament supply) rated for 5Y3/5AR4 current draw (2.0 amps) according to the circuit design is good for a GZ33 with current draw of 3.0 amps? Very dangerous situation for those who are not aware of this limitation I would say. Did you check the filament transformer rating of the rectifier supply or noticed any change in heat from the filament transformer? If not the proper rating and noticed an increase in heat from the PT, turning ON/OFF the unit as frequent to avoid stress to the PSU is the last thing I would be concerned of. Another thing, the 5AR4 drops 17 V at 225 ma, the 5V4 is 25 Volts at 175 mA, the GZ33 being similar to the 5U4 drops 44 V at 225 mA for G/GA and 50 V at 275 mA for the GB. Not really the same (21/27 volts change!) and I bet that is why the change in sound because you are changing the OP of the tubes. A Mullard GZ33 cost a lot. It seems that a 25W aluminum ohmite dropping resistor on the B+ line will work also no? Do you have a measurements of the B+ from GZ34 to GZ33 and see the difference? Since you are being adventurous, what is the reason why you did not try a 5U4? |
Hello Ait,
Oh, do not get me wrong, I am just curious following your experiment. Yes, I am aware that your unit is not stock anymore. The same reason why I asked if you know the rating of the rectifier filament supply.
Yes, you are right, on the manual the GZ37 is listed as "ok" replacement of a 5AR4. He also listed a GZ32 but not a GZ33 or a 5U4. That is my point. I thought the GZ37 has a current draw of 2.8 amps max, 200 mA amps difference from a GZ33 (with 3 amps).
regards,
Abe |
No argument here as far as rolling the rectifier. Yes, no signal goes to it except the dc voltage it provides is the whole signal that is amplified. Besides, your unit is different now compared to stock. Let's say your preamp is a new design using the psu of a Supratek preamp and any experiment you have may or may not be applicable to stock Chenin's.
Oh well, as long as u have fun doing what you are doing.
Regards,
|
By the way, the Radio Museum site lists the current draw of the GZ33 as 2.8 amps, same as the GZ37 Hmmmm......different on mine. I thought the 5U4 is the same as a GZ33, current draw-wise, and the GZ37 is 200 mA less. GZ37GZ33regards |
There you go, it is settled. Let the GZ33 frenzy begin!
No problem here. Besides, my all stock Supratek Chenin is in the corner of my listening room collecting dust for almost 10 months now and counting. I was hoping a little bit that it becomes a collectors item in the future. We'll see...
regards |
Bbro,
I had the same experienced. I thought the Supratek synergized very well with planars and electrostatics, be it driven by SS or tube amps. That was my impressions when I had my Martin Logans and Magnepans.
regards,
Abe |
Have you tried it with no source connected? Do you hear it when using phono only? Is it a "bleed through" or constant magnitude in sound.
From the manual: " You may notice some "bleed through" of the tuner or other auxiliaries when the phono is in operation. This is because of the very high gain of the phono stage and also because shielded wire is deliberately not used for the other inputs because of its sound degrading qualities...."
|
I too have the same Supratek Preamp, Chenin, since 2004!
I build my own amps and other preamps so it was so easy for me to tweak it but I cannot do it as I want to preserve its own "tone" that I have been accustomed to for so many years sinced I owned the unit.
I enjoyed, and still enjoying, my preamp to this date and I am still very pleased on how it sounds especially with my horn/SET based system. Much better sounding to me when I had SS or PP tube amps and conventional or active speakers.
Thanks guys for |
