Question About Using Tubes In Phono Section In A Receiver While Using A Phono Pre-Amp

jgannon

AK Subscriber
Subscriber
If I am bypassing the phono section of a receiver by using a phono pre, do I need a tube in the phono section of the receiver?

OR -

If I do have to use a tube in the phono section while I am using the phono pre, should I just put a cheap tube in there? I was thinking, instead of using an old Mullard or RCA Blackplate 12ax7 in the phono section, I could use any old tube there and save the better 12ax7s if they are being completely overridden by the phono preamp..
 
Never should a tube unit be run without its full tube compliment in place.

Certainly nothing wrong with swapping tubes with others of the same type.
 
Never should a tube unit be run without its full tube compliment in place.

Certainly nothing wrong with swapping tubes with others of the same type.

Yeah, I kinda figured that about not using a tube! But if I'm using a phono pre, will using a really good sounding tube in the phono section of the receiver help the overall sound while using a phono pre? Or will the tube in that position then have no affect on the sound?
 
Yeah, I kinda figured that about not using a tube! But if I'm using a phono pre, will using a really good sounding tube in the phono section of the receiver help the overall sound while using a phono pre? Or will the tube in that position then have no affect on the sound?

Which inputs on the receiver will you be using for making the connections from the phono preamplifier - the AUX or PHONO?
 
I was told by the Tech i use for my tube gear to put in cheap tubes in the phono section if i was wasnt using it and using a phono pre. i do use my phono sections as well as a pre so ive got tele's in my fisher and bugle boys in my 7C so i couldnt say for sure if it would affect the sound but i dont think it does.
 
Then the choice of tube(s) in the phono section of the receiver will have no effect since you will not be using that signal path.

Cool, that's what I thought.

Next to the 12ax7 in the phono position of the amp (it's a Fisher TA-500) there is a 12ax7 that is used for the tone controls. I guess though, that that tube would still have an affect on the sound.
 
Sovtek 12ax7lps is cheap.

Most would assume you want your amp running as designed with its full tube set. 30 bucks for a pair of the above.
 
Last edited:
I was told by the Tech i use for my tube gear to put in cheap tubes in the phono section if i was wasnt using it and using a phono pre. i do use my phono sections as well as a pre so ive got tele's in my fisher and bugle boys in my 7C so i couldnt say for sure if it would affect the sound but i dont think it does.

Oh, meaning sometimes you don't use the pre-amps?
 
Never should a tube unit be run without its full tube compliment in place.

As with lots of things in life, "it depends!" I have a Heathkit AA-151 in which I disabled the phono section while making other modifications to the front-end. When those modifications were complete, the 2 6EU7s in question were no longer part of the signal path for line-level sources (they were before, hence the other front-end modifications), so I removed them (preferring not to keep a hard to find tube unnecessarily lit up). Of course, knowing how the circuit worked, I knew this was safe, and the heater supply voltages everywhere else also were within tolerance with the tubes removed.

If you have an integrated unit and you don't want to use its phono stage, and removing the tubes would not put the heater supply voltages out of spec everywhere else, and removing the tubes would not affect the signal path of other input sources, then removing the tubes would be OK.
 
As with lots of things in life, "it depends!" I have a Heathkit AA-151 in which I disabled the phono section while making other modifications to the front-end.

Since the OP made no mention of having modified his receiver, the logical assumption is that it had not been. Better to err on the side of caution as no harm would result by keeping the entire tube compliment in place, even had been so modified.

Some modern equipment even shuts down the phono section tubes altogether when it is not being used.
 
Next to the 12ax7 in the phono position of the amp (it's a Fisher TA-500) there is a 12ax7 that is used for the tone controls. I guess though, that that tube would still have an affect on the sound.

I would agree.
 
Yeah, I kinda figured that about not using a tube! But if I'm using a phono pre, will using a really good sounding tube in the phono section of the receiver help the overall sound while using a phono pre? Or will the tube in that position then have no affect on the sound?

If you are using a separate phono pre-amp, then you do NOT want to use the phono section of your receiver. The separate phono pre-amp is already applying RIAA equalization and amplifying the signal to line-level, so you would want to use e.g. the AUX input on your receiver.

Now, it's a different question about whether a nice or a crappy tube in that spot will make a difference with the pre-amplified phono signal coming into the AUX input. It depends on your receiver's line-level signal path. I would say the common case would be "no, it won't make any difference", but that's certainly not universal; see my comment about Heathkit AA-151 above. In that unit, to simplify source switching, the line-level inputs were attenuated and then routed through the second half of each channel's phono section (but not through the RIAA equalization network).
 
If you are using a separate phono pre-amp, then you do NOT want to use the phono section of your receiver. The separate phono pre-amp is already applying RIAA equalization and amplifying the signal to line-level, so you would want to use e.g. the AUX input on your receiver.

Now, it's a different question about whether a nice or a crappy tube in that spot will make a difference with the pre-amplified phono signal coming into the AUX input. It depends on your receiver's line-level signal path. I would say the common case would be "no, it won't make any difference", but that's certainly not universal; see my comment about Heathkit AA-151 above. In that unit, to simplify source switching, the line-level inputs were attenuated and then routed through the second half of each channel's phono section (but not through the RIAA equalization network).

I see what you're saying. Maybe some of the guys in the Fisher forum who know these particular amps would know if this would be an issue. But maybe like you say, ordinarily what tube you would use in the phono section wouldn't make any difference.
 
What is the receiver?

I tried using my Hagerman Bugle 2 phono pre with it, and I liked the sound. I've been using some old Mullards and RCA blackplates in the receiver, and I was thinking, why waste them if they aren't affecting the sound
 
Back
Top Bottom