Changing pre-amp tubes

[jt1stcav]

Tube rolling definately makes a difference (for the better), but no amount of tube rolling, even with the quietest-known tubes, will totally reduce or elliminate any or all hiss IMO. My 6SN7 SRPP line stage preamp is extremely quiet, both with the stock Chinese military tubes and my NOS '50s vintage RCA and Mullard tubes in place...Like others have stated, if my ear is up against the tweeter's horn, I can still detect some hiss, but when seated at my listening position, I cannot hear anything except the music, even at the quietest of passages! So I also agree that you may have other problems with your preamp that different tubes may not correct...hopefully something that can be repaired inexpensively. Nothing worse than putting up with hiss that distracks you from enjoying your music, especially during the softest parts!

Good luck...hope you find the problem!

[NOSValves]

Is this Hiss equal out of both channels ? This amp blew 2 preamp tubes ?? Wow that is a new one.

Do this !!!

Take the 2 right 12AX7 tubes (the ones under the shields) and switch them with the 2 left 12AX7 (again under the shields) If there is no change in this hiss your hearing while using the AUX input with a CD player connected and paused then something is almost definitely wrong with the amp or your hookups. On AUX setup as above with the volume turned to 2:00 you should not get any noise that is audible unless your ear is right up to the speakers. If you do there is absolutely something wrong somewhere. The RF-35 is not that efficient when talking Klipsch speakers.

Craig

[doctorcilantro]

NOSvalves, thanks I tried that and then put in three black plate rca's and two tele's....same result with cd player and a dj mixer. My wife can hear the hiss at 2:00 at 13 feet ...at that distance it is "subtle" but at half that it is plain tough to bear. I just turned the amp on again and from the couch (13') to me it is not subtle. I turn on a Miles cd and while the cd his its own noise, when coupled with the amp's hiss it gets purdy loud. The rightmost AX7 is a telefunken and it starts to whining as my finger gets near it ...if I touch it it howls. I wonder if it's the tube or the socket ...I'll have to check. The 7199 just beind it seems to respond to a light tap like none of the other tubes, it too sounds off but not like the tele.

Jon

[NOSValves]

Okay now I'm curious ! What is this DJ mixer deal ? You really need to try a isolate if the problem is in the amp or if it is possibly a source problem. You say this amp is on Tuner/Aux or LP's and about the same on all. Do you happen to have a old set of junk RCA interconnects that you could careless if you ruin just to make sure there isn't a source problem ? If you do just simple cut the wire off about 6" from the RCA and strip the wire insulation off carefully from the shielding and the inner conductor about 3/4" will do of bare wire. Then twist them together. Do this for left and RCA connectors plug this contraption into the AUX input which will ground out the input also do not have any other inputs connect no turn table no tuner just these shorting plugs. Turn the amp on and if there is any noise it is the amp making it. There should almost nothing at zero volume with your ear to the speaker and very little with the volume at 75%. If the hiss is still there the amp is defective and needs repair no other option here.

Craig

[doctorcilantro]

I like to use the DJ mixer because I have so many sources.

When I plug in the cd player to the Sherwood AUX input I am getting a lot more gain for a couple reasons.

I was using the REC out of the DJ mixer not the MASTER to avoid any amplification and overload of the Sherwood preamp. I was only rasing sliders to 7 (which is marked for use with Master). Now I see that for the mixer to have equal gain as the cd player the sliders have to go to ten.

So....I haven't been able to try shorting yet, but my ratios were all screwy. I will set the volume as mdeen suggested and then try the cd player directly hooked up to the amp and then through the DJ mixer. If I raise the sliders on the dj mixer to equal what I was hearing with the the direct cd connection I should be okay. Ryan says this is a high gain high impedance amp and when it was directly connected to the amp I couldn't turn the dial to 2:00...just too loud.

My turntable cart is a high ouput moving coil so of course I am getting not much as much gain out of the phono stage as I'd like but it's good enough.

Others have commented that they have no hiss at all even with the gain cranked to max. I wonder if my experience is just inherent to this amp.

Jon

[NOSValves]

I would do the shorting plug just to confirm where this noise is coming from. This will give a absolute confirmation if its the amp or the source ! The easiest path to diagnose a problem is to isolate all components from the chain then add them back one at a time. What is the output of your MC cartridge and what cartridge is it ? Just did a quick search and its 2mV from what I read no vintage amp is going to do well with that low of a output my 2.5mV MC doesn't do well with then either and will put me in the hiss zone of a tube vintage phono section for reasonable volume. But this has nothing to do with the AUX input.

Craig

[doctorcilantro]

Craig,

Yeah it's a 2mv I believe. I can try that shorting plug tonight. Can I use a cheapy RCA that came with my denon cd player? Or do I need something more substantial?

So do you still think I shouldn't be having as much noise? It starts at about 12 faintly, but at 2:00 you can hear it clearly from across the room 13-14 ft.

Also, what is up with the TAPE input...is this for an ultra low signal.....it seems to have an ENORMOUS amount of gain...more than the phono stage!!!! Wonder if I could use it for that?

I really love my X5-MC and I like this Sherwood even though seperates would have probably been less of a headache or $$$.

thanks,

JC

[NOSValves]

Yup the cheapy is prefect ! Just cut it 6" back and splice the wires together to create a short or grounding effect. If your at all confused email me your number/best time and I'll call you later !

If the tape input is for a Tape head then yes it has enomuos gain like a phono input and with a high level input (CD Player) it should distort horribly. If its a normal tape loop that it should be just like AUX and you have another problem.

Craig

[doctorcilantro]

Thanks, I'll look at your past post and figure it out; if I can't I'll be in touch.

I tried the REC out of the mixer but it was too much for it. Does it have more gain or less than the phono stage? I think it is not a normal tape loop as ryan mentioned that before.

thanks

Jon

[NOSValves]

Sounds like a tape head (low level) input to me. Send me a schematic if you have one. I have the S5000 II schematic and it shows a Tape Head input and a Record Output (strange thing to call it) and Monitor output (strange thing to call it). One of the two outputs should be a hign level input I would guess.

Edit

I don't think this amp has a tape loop in the normal sense from what I see tracing these strange Record/Monitor Ouputs . I see no reason why this amp could not be near dead silent though. In fact these are known to be really nice amps.

Craig