Custom Shop 50 bias voltage.

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swara
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Custom Shop 50 bias voltage.

Post by swara » Mon Apr 16, 2018 4:38 am

Hi all-
Can anyone tell me the proper bias voltage in a CS 50?
At pin(s)1/8 I get 1.2mv which seems pretty small to me.

Also- I haven't powered the amp up in my home in years, but when I did recently, the power
transformer sounds like a noisy ballast in a fluorescent lamp.
I might be sensitized to this as I've been building HiFi tube amps that are ultra quiet.

cheers.

Edit: After looking around the web and forum, I did see on the inside of the chassis of the AD and Retro 50(s) that the bias voltage at pin 5 is -32v. Is that the same for the Custom Shop 50? A little bit of a "buzz kill" not to find any writing inside. Ah well, had the amp for five years and this is the first time I've opened her up...
Also- I guess VTA/Dynaco designs are quite different from Orange as far as where bias measurements are taken...
Face palm!

bclaire
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Re: Custom Shop 50 bias voltage.

Post by bclaire » Mon Apr 16, 2018 4:36 pm

Hi - welcome to the forum.

We err on the side of not encouraging people to do their own biasing since we don't know anyone's electrical knowledge or whether they're 8 or 80.

Personally, I have no idea but maybe someone who does could PM you with the info.

swara
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Re: Custom Shop 50 bias voltage.

Post by swara » Mon Apr 16, 2018 6:19 pm

bclaire wrote:
Mon Apr 16, 2018 4:36 pm
Hi - welcome to the forum.

We err on the side of not encouraging people to do their own biasing since we don't know anyone's electrical knowledge or whether they're 8 or 80.

Personally, I have no idea but maybe someone who does could PM you with the info.
Thanks for your input. Yes, not knowing one's background with these things might make one not want to offer much advice. I've built several tube amps and have been working on my own for several decades so I do know my way around to some degree. Enough to make a simple bias adjustment. (Keep one hand in the back pocket while inside a "hot" amp!)
My wife thinks I'm 12 even though I have better than half a century under my skin! :lol: :lol: :lol:

Jondog
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Re: Custom Shop 50 bias voltage.

Post by Jondog » Mon Apr 16, 2018 6:31 pm

swara wrote:
Mon Apr 16, 2018 4:38 am
Hi all-
Can anyone tell me the proper bias voltage in a CS 50?
At pin(s)1/8 I get 1.2mv which seems pretty small to me.

Also- I haven't powered the amp up in my home in years, but when I did recently, the power
transformer sounds like a noisy ballast in a fluorescent lamp.
I might be sensitized to this as I've been building HiFi tube amps that are ultra quiet.

cheers.

Edit: After looking around the web and forum, I did see on the inside of the chassis of the AD and Retro 50(s) that the bias voltage at pin 5 is -32v. Is that the same for the Custom Shop 50? A little bit of a "buzz kill" not to find any writing inside. Ah well, had the amp for five years and this is the first time I've opened her up...
Also- I guess VTA/Dynaco designs are quite different from Orange as far as where bias measurements are taken...
Face palm!
I have no idea, but please post any info you find out. Also if you come across a schematic, send me a message!
Image

swara
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Re: Custom Shop 50 bias voltage.

Post by swara » Mon Apr 16, 2018 7:45 pm

Jondog wrote:
Mon Apr 16, 2018 6:31 pm


I have no idea, but please post any info you find out. Also if you come across a schematic, send me a message!
Will do. The schematic will be tough. I'm not sure how willing or legally able an authorized repair shop would be to give one out.

As far as bias voltages go- The original tubes at pin(s) 1/8 were 1.2mv. At pin 5 (as written inside the Retro and AD 50s) was @ -35v. Unfortunately when I took this reading, I was unaware that pin 5 was where you take a reading in Oranges. I was going on my experience with Dynaco designs.

Both the Retro and AD 50s say to set at -32v from pin 5. At pins 1/8 in my CS 50 this gives a reading of 0.9-1.0mv.

So there is a bit of difference between the two.

Next step is to call a service place, but they generally don't like to give out this info for the same reason that was mentioned earlier.

fiveightandten
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Re: Custom Shop 50 bias voltage.

Post by fiveightandten » Mon Apr 16, 2018 8:06 pm

Forget the factory bias recommendation. Set the bias how it sounds best to you, within the operating limits set by the manufacturer of the tubes you’re using.

This will be expressed in plate dissipation wattage, which takes the whole operation of the tube into account. Setting only using the negative voltage number isn’t something I’d recommend.

Industry standard is to set to around 70% of the recommended max, but you can go colder, or close to the max if you like the sound (at the expense of tube life and reduced reliability).
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'71 GRO100 || '96 OR-80 || AD30 || '64 AC-50 || AC-30TBX || Hiwatt DR504 || HI-TONE HT30
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swara
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Re: Custom Shop 50 bias voltage.

Post by swara » Tue Apr 17, 2018 4:39 pm

fiveightandten wrote:
Mon Apr 16, 2018 8:06 pm
Forget the factory bias recommendation. Set the bias how it sounds best to you, within the operating limits set by the manufacturer of the tubes you’re using.

This will be expressed in plate dissipation wattage, which takes the whole operation of the tube into account. Setting only using the negative voltage number isn’t something I’d recommend.

Industry standard is to set to around 70% of the recommended max, but you can go colder, or close to the max if you like the sound (at the expense of tube life and reduced reliability).
That reminds me of when I repaired instruments for a living. Many of my clients were aircraft machinists, who were "by the numbers" guys. When I'd set up their guitars, it could not be by "feel"; they'd have none of that. So I'd have to speak in terms of "thousandths" at particular frets and string tensions in PSI... etc.
I've been spending a lot of time working on audio amps where biasing is viewed a little differently. Though recently, I had a quad of Psvane KT120s that would not bias "by the numbers".
Ah well...
I am surprised at what little there is out there about the CS50 though. Given that I also want to replace a very noisy power transformer, it's downright frustrating.

Jondog
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Re: Custom Shop 50 bias voltage.

Post by Jondog » Tue Apr 17, 2018 5:30 pm

swara wrote:
Tue Apr 17, 2018 4:39 pm
fiveightandten wrote:
Mon Apr 16, 2018 8:06 pm
Forget the factory bias recommendation. Set the bias how it sounds best to you, within the operating limits set by the manufacturer of the tubes you’re using.

This will be expressed in plate dissipation wattage, which takes the whole operation of the tube into account. Setting only using the negative voltage number isn’t something I’d recommend.

Industry standard is to set to around 70% of the recommended max, but you can go colder, or close to the max if you like the sound (at the expense of tube life and reduced reliability).
That reminds me of when I repaired instruments for a living. Many of my clients were aircraft machinists, who were "by the numbers" guys. When I'd set up their guitars, it could not be by "feel"; they'd have none of that. So I'd have to speak in terms of "thousandths" at particular frets and string tensions in PSI... etc.
I've been spending a lot of time working on audio amps where biasing is viewed a little differently. Though recently, I had a quad of Psvane KT120s that would not bias "by the numbers".
Ah well...
I am surprised at what little there is out there about the CS50 though. Given that I also want to replace a very noisy power transformer, it's downright frustrating.
Good chance the power transformer is the same as the Rockerverbs, which you can get a direct replacement from Mercury Magnetics. You might check the caps or other sources before you do that though.
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fiveightandten
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Re: Custom Shop 50 bias voltage.

Post by fiveightandten » Tue Apr 17, 2018 5:53 pm

swara wrote:
Tue Apr 17, 2018 4:39 pm
fiveightandten wrote:
Mon Apr 16, 2018 8:06 pm
Forget the factory bias recommendation. Set the bias how it sounds best to you, within the operating limits set by the manufacturer of the tubes you’re using.

This will be expressed in plate dissipation wattage, which takes the whole operation of the tube into account. Setting only using the negative voltage number isn’t something I’d recommend.

Industry standard is to set to around 70% of the recommended max, but you can go colder, or close to the max if you like the sound (at the expense of tube life and reduced reliability).
That reminds me of when I repaired instruments for a living. Many of my clients were aircraft machinists, who were "by the numbers" guys. When I'd set up their guitars, it could not be by "feel"; they'd have none of that. So I'd have to speak in terms of "thousandths" at particular frets and string tensions in PSI... etc.
I've been spending a lot of time working on audio amps where biasing is viewed a little differently. Though recently, I had a quad of Psvane KT120s that would not bias "by the numbers".
Ah well...
I am surprised at what little there is out there about the CS50 though. Given that I also want to replace a very noisy power transformer, it's downright frustrating.
If you’re a ‘by the numbers’ guy, you should steer clear of bias recommendations supplied by a manufacturer (unless you are getting your tubes from them). I’m sure you know this given your experience, but every set of tubes draws a different amount of current. Setting by negative voltage is a fairly inaccurate and imprecise method of setting bias.

Orange may spec their tube supply to be within a certain range of current draw, and thus be able to set the amps up within reason based on a single negative voltage reading. But unless you have that same luxury (and know what their tube spec and variance is), that negative voltage number isn’t very useful.

As I mentioned, biasing by plate dissipation wattage is the best “by the numbers” method without utilizing specialized equipment. This is what the vast majority of techs are doing, and it is in no way inferior to blindly setting the amp up based on a manufacturer spec. My 1964 Vox AC-50 has a published negative voltage spec to set the bias. Guess what would happen if I followed it. You are far better off using your expertise to bias the amp properly, by ear, within the limits of the tubes you’re using. This is the correct way to do it. It’s a guitar amp. The goal is best possible sound within the limits of the tubes.

Regarding the power transformer; you mentioned the amp had been sitting for a few years. The filter caps may just need to reform a little through use, and may be stressing the PT. I’d give it a few hours of healthy high volume use before you start to worry about the power transformer.

If it does need to be replaced, I’d contact Orange. I’m sure they’d be willing to supply test point specs, at the very least, to an experienced tech.
Image
'71 GRO100 || '96 OR-80 || AD30 || '64 AC-50 || AC-30TBX || Hiwatt DR504 || HI-TONE HT30
LP Standard || LP Studio || LP Custom Lite || Ric 620 || Ric 360 || MIA Tele || SG 61 RI

swara
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Location: Paauilo, Hawaii

Re: Custom Shop 50 bias voltage.

Post by swara » Tue Apr 17, 2018 11:47 pm

fiveightandten wrote:
Tue Apr 17, 2018 5:53 pm
swara wrote:
Tue Apr 17, 2018 4:39 pm
fiveightandten wrote:
Mon Apr 16, 2018 8:06 pm
Forget the factory bias recommendation. Set the bias how it sounds best to you, within the operating limits set by the manufacturer of the tubes you’re using.

This will be expressed in plate dissipation wattage, which takes the whole operation of the tube into account. Setting only using the negative voltage number isn’t something I’d recommend.

Industry standard is to set to around 70% of the recommended max, but you can go colder, or close to the max if you like the sound (at the expense of tube life and reduced reliability).
That reminds me of when I repaired instruments for a living. Many of my clients were aircraft machinists, who were "by the numbers" guys. When I'd set up their guitars, it could not be by "feel"; they'd have none of that. So I'd have to speak in terms of "thousandths" at particular frets and string tensions in PSI... etc.
I've been spending a lot of time working on audio amps where biasing is viewed a little differently. Though recently, I had a quad of Psvane KT120s that would not bias "by the numbers".
Ah well...
I am surprised at what little there is out there about the CS50 though. Given that I also want to replace a very noisy power transformer, it's downright frustrating.
If you’re a ‘by the numbers’ guy, you should steer clear of bias recommendations supplied by a manufacturer (unless you are getting your tubes from them). I’m sure you know this given your experience, but every set of tubes draws a different amount of current. Setting by negative voltage is a fairly inaccurate and imprecise method of setting bias.

Orange may spec their tube supply to be within a certain range of current draw, and thus be able to set the amps up within reason based on a single negative voltage reading. But unless you have that same luxury (and know what their tube spec and variance is), that negative voltage number isn’t very useful.

As I mentioned, biasing by plate dissipation wattage is the best “by the numbers” method without utilizing specialized equipment. This is what the vast majority of techs are doing, and it is in no way inferior to blindly setting the amp up based on a manufacturer spec. My 1964 Vox AC-50 has a published negative voltage spec to set the bias. Guess what would happen if I followed it. You are far better off using your expertise to bias the amp properly, by ear, within the limits of the tubes you’re using. This is the correct way to do it. It’s a guitar amp. The goal is best possible sound within the limits of the tubes.

Regarding the power transformer; you mentioned the amp had been sitting for a few years. The filter caps may just need to reform a little through use, and may be stressing the PT. I’d give it a few hours of healthy high volume use before you start to worry about the power transformer.

If it does need to be replaced, I’d contact Orange. I’m sure they’d be willing to supply test point specs, at the very least, to an experienced tech.
As I had mentioned, I had a similar experience with a quad of Psvane KT120s in an audio amp. Recommended bias voltage at pin 8 was .50v and all kinds of unpleasant things started to happen at anything beyond .25v.
Interesting to learn new things though. Different angles.

fiveightandten
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Posts: 3729
Joined: Sat Apr 05, 2003 6:18 pm
Location: Connecticut, USA

Re: Custom Shop 50 bias voltage.

Post by fiveightandten » Wed Apr 18, 2018 3:15 am

swara wrote:
Tue Apr 17, 2018 11:47 pm
fiveightandten wrote:
Tue Apr 17, 2018 5:53 pm
swara wrote:
Tue Apr 17, 2018 4:39 pm


That reminds me of when I repaired instruments for a living. Many of my clients were aircraft machinists, who were "by the numbers" guys. When I'd set up their guitars, it could not be by "feel"; they'd have none of that. So I'd have to speak in terms of "thousandths" at particular frets and string tensions in PSI... etc.
I've been spending a lot of time working on audio amps where biasing is viewed a little differently. Though recently, I had a quad of Psvane KT120s that would not bias "by the numbers".
Ah well...
I am surprised at what little there is out there about the CS50 though. Given that I also want to replace a very noisy power transformer, it's downright frustrating.
If you’re a ‘by the numbers’ guy, you should steer clear of bias recommendations supplied by a manufacturer (unless you are getting your tubes from them). I’m sure you know this given your experience, but every set of tubes draws a different amount of current. Setting by negative voltage is a fairly inaccurate and imprecise method of setting bias.

Orange may spec their tube supply to be within a certain range of current draw, and thus be able to set the amps up within reason based on a single negative voltage reading. But unless you have that same luxury (and know what their tube spec and variance is), that negative voltage number isn’t very useful.

As I mentioned, biasing by plate dissipation wattage is the best “by the numbers” method without utilizing specialized equipment. This is what the vast majority of techs are doing, and it is in no way inferior to blindly setting the amp up based on a manufacturer spec. My 1964 Vox AC-50 has a published negative voltage spec to set the bias. Guess what would happen if I followed it. You are far better off using your expertise to bias the amp properly, by ear, within the limits of the tubes you’re using. This is the correct way to do it. It’s a guitar amp. The goal is best possible sound within the limits of the tubes.

Regarding the power transformer; you mentioned the amp had been sitting for a few years. The filter caps may just need to reform a little through use, and may be stressing the PT. I’d give it a few hours of healthy high volume use before you start to worry about the power transformer.

If it does need to be replaced, I’d contact Orange. I’m sure they’d be willing to supply test point specs, at the very least, to an experienced tech.
As I had mentioned, I had a similar experience with a quad of Psvane KT120s in an audio amp. Recommended bias voltage at pin 8 was .50v and all kinds of unpleasant things started to happen at anything beyond .25v.
Interesting to learn new things though. Different angles.
Indeed. Tube sets differ, wall voltages differ. Actually, I have 2 AD30s, and the power transformers put out wildly different voltages plugged into the same socket with the same tubes. Neither amp is on spec.

Let us know how you make out with that PT.
Image
'71 GRO100 || '96 OR-80 || AD30 || '64 AC-50 || AC-30TBX || Hiwatt DR504 || HI-TONE HT30
LP Standard || LP Studio || LP Custom Lite || Ric 620 || Ric 360 || MIA Tele || SG 61 RI

swara
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Location: Paauilo, Hawaii

Re: Custom Shop 50 bias voltage.

Post by swara » Wed Apr 18, 2018 3:35 am

fiveightandten wrote:
Wed Apr 18, 2018 3:15 am
Let us know how you make out with that PT.
Oh that... :lol: :lol: :lol:
Yeah, for the "crank it" for the caps I'll need to grab an attenuator of sorts.
Though there is rust on the plates which a local tech said could create an issue if it's an indicator of moisture getting in between them.
The amp did live in Hawaii for several years which is tough on amps among other things...
So the adventure begins...

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