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Posted
2 minutes ago, RockRolley said:

I know of somebody with a Goldenage phono stage who had a few mods done (not by Duc) which reduced the volume-along with whatever the mood was supposed to achieve. Is yours stock? 

Simon, I'm not sure of that.  I just need to source a rectifier tube and 2 x 6CG7 tubes.  I have already replaced the 12AT7 tubes.  What rectifier tube are you using on yours.  Mine has a 5AR4 Phillips US.

I had never heard of a 6CG7 tube and I have been around tubes for a very long time.

Posted

 Hey, @mwhouston and @aussievintage, you guys know toobs.

 

Am I correct in thinking the gain from a tube gain stage is determined by (as well as the 'Mu' of the tube used) the value of a resistor ... or the ratio of two resistor values?

 

If so, I would've thought it should be possible to increase the gain of @vinyl-62's DUC phono stage?

 

Posted
1 hour ago, vinyl-62 said:

Simon, I'm not sure of that.  I just need to source a rectifier tube and 2 x 6CG7 tubes.  I have already replaced the 12AT7 tubes.  What rectifier tube are you using on yours.  Mine has a 5AR4 Phillips US.

I had never heard of a 6CG7 tube and I have been around tubes for a very long time.

GZ34 for mine. Just plugged in. Using inbuilt MC, however not ideal loading or gain for my lo MC Benz cart, so maybe a little quieter than if I had it Andy’s head amp in, but still not a concerning level, easy to get a great level, so I’d say in terms of characteristics the Goldenage isn’t so low that there should be issues. Having said that, my Weston wasn’t very high gain, maybe the combo could prove problematic? 

IMG_2690.jpeg

Posted
4 minutes ago, andyr said:

Am I correct in thinking the gain from a tube gain stage is determined by (as well as the 'Mu' of the tube used) the value of a resistor ... or the ratio of two resistor values?

 

If you are thinking along the lines of an opamp, where gain is determined by the ratio of the feedback resistors, then no.    Valve amplifiers tend to just have one global feedback, and yes, that can be fiddled to adjust overall gain, but it is uncommon to see this applied around just one gain stage.  They work "open loop" and so gain is determined by the valve choice and, to a lesser extent biasing.  This is why you can use a 12AX7 for about 100x gain, or a 12AU7 for a lot less, or a 12AT7 for somewhere in between, all in (usually) the same circuit.  It's not the circuit determining the gain, but the inherent characteristics of the valve.

Posted

Thanks, @aussievintage.  I was actually thinking of my jfet-based 'Muse' phono stage - where gain for each gain-stage is determined by:

  1. the gain resistor, and
  2. the current flowing through the jfets.

But from what you said ... it would seem the gain of Duc's phono stage might be able to be altered by tube choice?

 

  • Like 1

Posted
Just now, andyr said:

Thanks, @aussievintage.  I was actually thinking of my jfet-based 'Muse' phono stage - where gain for each gain-stage is determined by:

  1. the gain resistor, and
  2. the current flowing through the jfets.

But from what you said ... it would seem the gain of Duc's phono stage might be able to be altered by tube choice?

 

 

unless he uses global feedback

Posted

I was reading some time ago ,of a hi end valve phono stage 

and indeed ,gain was determined by what valves you used ,

and gave you a b or c valve ,gain characteristics ,

to find the one that would suite the end user 

  • Like 1
Posted (edited)
4 hours ago, vinyl-62 said:

Simon, I'm not sure of that.  I just need to source a rectifier tube and 2 x 6CG7 tubes.  I have already replaced the 12AT7 tubes.  What rectifier tube are you using on yours.  Mine has a 5AR4 Phillips US.

I had never heard of a 6CG7 tube and I have been around tubes for a very long time.

 

The 6CG7 tube was the successor tube to the 6SN7 tube but in 9-pin mini format. It's a very common tube used in many tube circuits (CJ gear, etc.). The 6FQ7 can also be used in its place. A GZ34 (European designation) and 5AR4 (US designation) are the exact same rectifier tube. You can use other 5V rectifiers such as the 5R4GY and 5V4G/GZ32 tube in its place to change the tonal characteristics of the unit.

 

I suspect if you have a deficiency in gain it may be related to the 12AT7 tube. You can try a 12AX7 in its place to see if that makes any difference as the amplification factor (mu) will increase from 60 to 100.

Edited by xlr8or
  • Like 4
Posted
4 minutes ago, xlr8or said:

 

The 6CG7 tube is the successor tube to the 6SN7 tube but in 9-pin mini format. It's a very common tube used in many tubes circuits (CJ gear, etc.). The 6FQ7 can also be used in its place. A GZ34 (European designation) and 5AR4 (US designation) are the exact same rectifier tube. You can use other 5V rectifiers such as the 5R4GY and 5V4G/GZ32 tube in its place to change the tonal characteristics of the unit.

 

I suspect if you have a deficiency in gain it may be related to the 12AT7 tube. You can try a 12AX7 in its place to see if that makes any difference as the amplification factor (mu) will increase from 60 to 100.

 

There you are, @vinyl-62!  👍

 

  • Like 1
Posted
1 hour ago, xlr8or said:

 

The 6CG7 tube is the successor tube to the 6SN7 tube but in 9-pin mini format. It's a very common tube used in many tubes circuits (CJ gear, etc.). The 6FQ7 can also be used in its place. A GZ34 (European designation) and 5AR4 (US designation) are the exact same rectifier tube. You can use other 5V rectifiers such as the 5R4GY and 5V4G/GZ32 tube in its place to change the tonal characteristics of the unit.

 

I suspect if you have a deficiency in gain it may be related to the 12AT7 tube. You can try a 12AX7 in its place to see if that makes any difference as the amplification factor (mu) will increase from 60 to 100.

Thank you very much for this information.  I will try some 12AAX7 tubes tomorrow and report back.  I think I also have some GZ32 tubes to try.

  • Like 1

Posted
9 hours ago, vinyl-62 said:

Thank you very much for this information.  I will try some 12AAX7 tubes tomorrow and report back.  I think I also have some GZ32 tubes to try.

Keep in mind, a cricuit designed for 12AT7s may exceed some limits of a 12AX7.  Was this circuit designed for 12AT7s and is it approved for 12AX7s?

 

Note the differences - particularly  Wa and Ik limiting values.

 

image.png.58a73648ab90b5ad8cdc1f8b0604b94d.png

 

image.png.d02d4ca87bf42a1469ca77ab4b7ee9a0.png

  • Like 1
Posted (edited)

@vinyl-62 The points raised by @aussievintage are quite valid. I initially  suggested trying a 12AX7 to see if that made any difference as an interim measure. From researching the build you have further it appears that previous sold units are configured to work with a 12AT7 input into a 6CG7 output buffer stage rectified by a GZ34. There could be some RIAA applied from the second triode stage of the 12AT7 or the first triode stage of the 6CG7 as the arrangement looks to be SRPP for the 2 channels. By all means try changing the GZ34 to a GZ32 to confirm the GZ34 is working properly. When a rectifier goes the output will normally be extremely weak. Please also note that a pair of tubes simultaneously being weak in output is not a regular occurrence. On digesting the above further you may have a SUT ratio mismatch issue.

Edited by xlr8or
  • Like 4
Posted

I found this email I received from Duc explaining the Reference phono-amp when I was ordering mine, many years ago. It might help. 
 

Golden Age Audio Reference
If you are going to use the MC cartridge, then you need an MC step up transformer, which we also made using Lundalh transformers from Sweden, of which we're a distrubutor of. it can be either build in step up transformers or build separately in our premium Tasmanian blackwood boxes . we can select the step up transformers to suit your need and build it in to the phono preamp or build in separate enclosure .
Valves used in the phono are
2 x 6CG7
2 x 12AT7/ ECC81
1x GZ34 or 5AR4 , 5V4G .
gain approximately 40Db in MM or 70Db in MC ,
2 x input for MM model and MM/MC input for MC model.
Chassis is Solid Blackwood with Anodised Aluminium top / bottom .
we also designed a new feet's machined from Solid Delrin with rubber ring insert .
dimension : 400 x 330 x 220mm
weight approx 35 bls .
price indicated below is for MM model
for MC model please add $850
price is $3300.00, which includeds all new old stock valves, that including NOS GZ34 or 5V4G rectifier , signal tubes supllied also NOS like GE,RCA or Mullard.
Delivery time will be approximately 2 months after you place your order and when the deposit is paid.
We only make them to order.

Sent from my iPhone

  • Like 4
Posted
2 minutes ago, frankn said:

I found this email I received from Duc explaining the Reference phono-amp when I was ordering mine, many years ago. It might help. 
 

Golden Age Audio Reference
If you are going to use the MC cartridge, then you need an MC step up transformer, which we also made using Lundalh transformers from Sweden, of which we're a distrubutor of. it can be either build in step up transformers or build separately in our premium Tasmanian blackwood boxes . we can select the step up transformers to suit your need and build it in to the phono preamp or build in separate enclosure .
Valves used in the phono are
2 x 6CG7
2 x 12AT7/ ECC81
1x GZ34 or 5AR4 , 5V4G .
gain approximately 40Db in MM or 70Db in MC ,
2 x input for MM model and MM/MC input for MC model.
Chassis is Solid Blackwood with Anodised Aluminium top / bottom .
we also designed a new feet's machined from Solid Delrin with rubber ring insert .
dimension : 400 x 330 x 220mm
weight approx 35 bls .
price indicated below is for MM model
for MC model please add $850
price is $3300.00, which includeds all new old stock valves, that including NOS GZ34 or 5V4G rectifier , signal tubes supllied also NOS like GE,RCA or Mullard.
Delivery time will be approximately 2 months after you place your order and when the deposit is paid.
We only make them to order.

Sent from my iPhone

Very helpful, thank you for posting this.  I will just change the rectifier tube this morning and report back.

Thanks

Chris

Posted
4 minutes ago, frankn said:


gain approximately 40Db in MM or 70Db in MC ,
 

 

Very interesting, Frank.

 

40dB is 100x gain - so that's what Duc's phono stage circuit delivers.  70dB in MC mode is 3160x gain ... so the SUT must be configured to produce gain of 3160 / 100  =  31.6x.  IE. a 1:32 SUT is used.

 

Posted

Just installed NOS Mullard GZ32 and I'm obtaining much more gain from the phonostage.  Next I will replace the 6CG7 tubes once I manage to purchase some and will see what happens.  I have only tried it with MC at this stage.

  • Like 1
Posted
3 minutes ago, vinyl-62 said:

Just installed NOS Mullard GZ32 and I'm obtaining much more gain from the phonostage.  

 

 @aussievintage / @mwhouston / @xlr8or ... not knowing much about tube circuits - can you explain to me how a rectifying tube can alter the circuit's gain?

 

Surely all it does is turn AC from the mains into DC for the circuit?  Sure, a different rectifying tube might output a higher DC voltage ... but why would that change the circuit's gain?

 

Posted
21 minutes ago, andyr said:

 

 @aussievintage / @mwhouston / @xlr8or ... not knowing much about tube circuits - can you explain to me how a rectifying tube can alter the circuit's gain?

 

Surely all it does is turn AC from the mains into DC for the circuit?  Sure, a different rectifying tube might output a higher DC voltage ... but why would that change the circuit's gain?

 

No it doesn’t amplifier but only rectifies. And rec tubes are greedy and eat some where between 30 and 50V DC. Not like our SS friends. Not forgetting there is a 1.4X bump up in voltage with full wave rec but then there’s the hair cut.

  • Thanks 1
Posted (edited)

Changing the rectifier valve will not change the gain. Some details of the preamplifier are given here    https://www.stereonet.com/forums/classifieds/item/8144-golden-age-audio-reference-phono-phono-preamplifier/            Since it is described as using passive equalising cct,s, swapping the 12AT7 to a 12AX7 valve will increase the gain but the anode and cathode resistors should be changed to ensure correct operating conditions. This assumes that the valves are used in a conventional class A set-up. There is a suggestion that a SRPP stage may have been used for the 6CG7 stage and if this is so, then this type of circuit is load fussy. Only an inspection of the circuits will reveal the answers.

Try  https://www.stereonet.com/forums/search/?q=Golden Age phono Preamplifier&quick=1

Edited by VanArn
Addition
Posted
48 minutes ago, andyr said:

 

 @aussievintage / @mwhouston / @xlr8or ... not knowing much about tube circuits - can you explain to me how a rectifying tube can alter the circuit's gain?

 

Surely all it does is turn AC from the mains into DC for the circuit?  Sure, a different rectifying tube might output a higher DC voltage ... but why would that change the circuit's gain?

 

 

In the extreme case of a worn out valve rectifier - maybe really low emission or something, or maybe only half of it is working - so half wave rectification -   the phono preamp may have been running on very low voltage.  Mu (gain) is fairly constant throughout the normal operating range, but not completely.  They even provide graphs to show how it changes. 

 

Still, hard to imagine any big gain changes under semi-reasonable conditions.  I am skeptical of the claim.

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  • Thanks 1

Posted
4 hours ago, frankn said:

I found this email I received from Duc explaining the Reference phono-amp

Awesome-that will be very useful for the ‘brains trust’/resources intent if this thread. Thank you 

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