SG 502 Assistance?


sweetbeats
 

Greetings everybody.

Hope this is an okay place to post this. I’m a member of the TM 500 group as well and will redirect this to there if advised.

I’ve been a member for some years but really essentially lurk as time to tinker with my audio and Tek gear is in limited to non-existent supply.

But the time has come to try and get my stuff working. I have a modest TM 500 setup…mainly using two TM 504 frames loaded with:

SC 502 (needs work…have a couple parts units)
DM 501A (dead…doesn’t appear to power up)
PS 503A (works!)
FG 502 (unknown commodity just yet)
AA 501A (seems to work!)
SG 502 (this seems to work too…more below)

I have additional modules, DC 504 (unknown commodity), an additional PS 503A, PS 501-1, DD 501, and too many mainframes…need to get rid of some…RTM 506, two spare TM 504, and two TM 503.

I want to use my TM 500 gear primarily to maintain/repair analog audio equipment.

Okay.

That’s the rundown.

So I’m working on the SG 502. It cleaned up nice, the frequency range buttons are a bit sticky, but the AA 501A says it is producing <0.004% THD from about 9Hz to 108kHz. Nice! The interesting thing is once you go outside of that range, like almost immediately, the distortion goes up considerably. Like…50% THD and higher. Are there any usual suspects I should address as a given with my SG 502 before doing anything else, or outside of that does anybody have any suggestions for a next step to helping it perform within spec across it’s designed frequency range (5Hz to 500kHz)?

Thanks!

Cory Oace


Jean-Paul
 

Check AA501 and SG502 specs, % THD varies with filters setting.

Jon


Jean-Paul
 

We can see the rated THD with all filters on and at max output of the pair ~ 0.0018%

Look at the residual output signal to see the distortion plus noise content

Jon


Tom Lee
 

I’d start by looking at the actual waveform. The specific way in which it distorts will be a useful clue.

Cheers
Tom

Sent from my iThing, so please forgive brevity and typos

On Jun 14, 2021, at 22:01, sweetbeats <torridheatstudios@gmail.com> wrote:

Greetings everybody.

Hope this is an okay place to post this. I’m a member of the TM 500 group as well and will redirect this to there if advised.

I’ve been a member for some years but really essentially lurk as time to tinker with my audio and Tek gear is in limited to non-existent supply.

But the time has come to try and get my stuff working. I have a modest TM 500 setup…mainly using two TM 504 frames loaded with:

SC 502 (needs work…have a couple parts units)
DM 501A (dead…doesn’t appear to power up)
PS 503A (works!)
FG 502 (unknown commodity just yet)
AA 501A (seems to work!)
SG 502 (this seems to work too…more below)

I have additional modules, DC 504 (unknown commodity), an additional PS 503A, PS 501-1, DD 501, and too many mainframes…need to get rid of some…RTM 506, two spare TM 504, and two TM 503.

I want to use my TM 500 gear primarily to maintain/repair analog audio equipment.

Okay.

That’s the rundown.

So I’m working on the SG 502. It cleaned up nice, the frequency range buttons are a bit sticky, but the AA 501A says it is producing <0.004% THD from about 9Hz to 108kHz. Nice! The interesting thing is once you go outside of that range, like almost immediately, the distortion goes up considerably. Like…50% THD and higher. Are there any usual suspects I should address as a given with my SG 502 before doing anything else, or outside of that does anybody have any suggestions for a next step to helping it perform within spec across it’s designed frequency range (5Hz to 500kHz)?

Thanks!

Cory Oace





EJP
 

Is this just on one frequency multiplier selection? If so I would get interested in the capacitors that get switched by it, C50-55.

But I agree you need to describe the waveform.

The later SG502s with the M34075 changes to the oscillator have much better THD+N than specified. Mine for example.

EJP


Eric
 

Cory,
It seems everything is working normally. The AA501 has an effective range of 10hz-22Khz (Human Hearing) but the AA501 and A will take in to account harmonics up to 300 Khz. But they don’t really make measurements that high as noted by the filters on the front panel. A weight and 80Khz Low pass. If you need to make measurements above 100 Khz you will need another instrument usually a Spectrum analyzer at that point. Also when it comes to the SG 502 and the 505 there are not many adjustments that can be made on the units so they don’t really drift out of spec. Now dirty switches will cause them to go nuts and make the outputs do funny things. But you can usually trust their distortion specs. Also, if you are trying to get to 500 Khz you are well outside the range of the AA501

For the stiff knob use and instrument grade oil. In my lab I have white lily sewing machine oil but I also have CRAIG instrument oil. A small amount on the brass reduction drive in the front and exercise the knob should get it freed right up. I will send you an e-mail off list with some additional information to some resources.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of sweetbeats
Sent: Tuesday, June 15, 2021 1:02 AM
To: TekScopes@groups.io
Subject: [TekScopes] SG 502 Assistance?

Greetings everybody.

Hope this is an okay place to post this. I’m a member of the TM 500 group as well and will redirect this to there if advised.

I’ve been a member for some years but really essentially lurk as time to tinker with my audio and Tek gear is in limited to non-existent supply.

But the time has come to try and get my stuff working. I have a modest TM 500 setup…mainly using two TM 504 frames loaded with:

SC 502 (needs work…have a couple parts units) DM 501A (dead…doesn’t appear to power up) PS 503A (works!) FG 502 (unknown commodity just yet) AA 501A (seems to work!) SG 502 (this seems to work too…more below)

I have additional modules, DC 504 (unknown commodity), an additional PS 503A, PS 501-1, DD 501, and too many mainframes…need to get rid of some…RTM 506, two spare TM 504, and two TM 503.

I want to use my TM 500 gear primarily to maintain/repair analog audio equipment.

Okay.

That’s the rundown.

So I’m working on the SG 502. It cleaned up nice, the frequency range buttons are a bit sticky, but the AA 501A says it is producing <0.004% THD from about 9Hz to 108kHz. Nice! The interesting thing is once you go outside of that range, like almost immediately, the distortion goes up considerably. Like…50% THD and higher. Are there any usual suspects I should address as a given with my SG 502 before doing anything else, or outside of that does anybody have any suggestions for a next step to helping it perform within spec across it’s designed frequency range (5Hz to 500kHz)?

Thanks!

Cory Oace


sweetbeats
 

Thank you so much, all, for the helpful replies!

Tom and EJP, yes, got it…I need to get my scope working (SC 502) if I want to know more about what the SG 502 across more of its range. Thanks. I need to get my scope working regardless.

Eric, thank you especially for your response. That makes perfect sense! I couldn’t see that forest for the trees (that I was asking the analyzer to do something outside ITS effective range)!

Regarding the “stiff knob”, it’s not a knob but rather the frequency and attenuation range push switches. Any suggestions?

Cory Oace


Eric
 

One other fun fact about the SG502 and 505's they are both outside the measurement range of my HP 4411B in terms of THD. It will only validate them down to 0.06% THD. But that is the limit of the 4411B. They really are incredible instruments.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of sweetbeats
Sent: Saturday, June 19, 2021 1:14 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] SG 502 Assistance?

Thank you so much, all, for the helpful replies!

Tom and EJP, yes, got it…I need to get my scope working (SC 502) if I want to know more about what the SG 502 across more of its range. Thanks. I need to get my scope working regardless.

Eric, thank you especially for your response. That makes perfect sense! I couldn’t see that forest for the trees (that I was asking the analyzer to do something outside ITS effective range)!

Regarding the “stiff knob”, it’s not a knob but rather the frequency and attenuation range push switches. Any suggestions?

Cory Oace


EJP
 

On Sat, Jun 19, 2021 at 11:45 PM, Eric wrote:

The AA501 has an effective range of 10hz-22Khz ...
That's not what it says in the specifcation. However my AA501 measures my SG502 at >= 50% THD from 124kHz, and the waveform looks perfectly clean, no different from 100KHz where it measures 0.190%. So Cory is at least not alone.

EJP


Eric
 

EJP,
If I am remembering the spec sheet correctly the aa501A is specified up to 100 Khz and measures harmonics up to 300Khz. But not a fundamental at 300 Khz. This would put the harmonics outside the range of the AA's. When you are looking at the wave form are you looking at the monitor out of the function out? function out is post notch filter and should be only be the distortion components. If you have sine waves on the function out the notch filter Is a little off. The monitor out is just a copy of what was on the input. It should always look good on a scope if not there is other issues that need to be addressed.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of EJP
Sent: Sunday, June 20, 2021 2:31 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] SG 502 Assistance?

On Sat, Jun 19, 2021 at 11:45 PM, Eric wrote:

The AA501 has an effective range of 10hz-22Khz ...
That's not what it says in the specifcation. However my AA501 measures my SG502 at >= 50% THD from 124kHz, and the waveform looks perfectly clean, no different from 100KHz where it measures 0.190%. So Cory is at least not alone.

EJP


sweetbeats
 

Thanks, Eric.

So here’s the trick, my SC 502 scope is n/f at this time so there has been no monitoring of the waveform. My intention is and has been to look at the waveform, but in the short term I wanted to at least learn if the SG 502 was producing anything and at what percent distortion, and knowing my AA 501A seems to be working I hooked things up and here we are.

Getting the scope working is next up.

Cory


Eric
 

Cory,
Good luck on the SC but be careful in there. It is 10 lbs of stuff in a 2lb box. Also it is a CRT so there is some places where there is sevral thousand volts. 4 - 7 - possibly 21KV it is needed to drive the tube. So take care.
Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of sweetbeats
Sent: Sunday, June 20, 2021 11:24 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] SG 502 Assistance?

Thanks, Eric.

So here’s the trick, my SC 502 scope is n/f at this time so there has been no monitoring of the waveform. My intention is and has been to look at the waveform, but in the short term I wanted to at least learn if the SG 502 was producing anything and at what percent distortion, and knowing my AA 501A seems to be working I hooked things up and here we are.

Getting the scope working is next up.

Cory


EJP
 

That is correct. Not 10-22KHz as you orginally wrote. Models vary but mine has a 22-22KHz filter: you don't have to use it.

It looks lke the nulling oscillator runs out of gas above 100KHz.

I miswrote earlier. My SG502 measures measures 0.0190% at 100KHz, not 0.190%. Measures 0.0078% with the 22KHz filter in ;-).

EJP


sweetbeats
 

Thanks again, Eric!

I will be careful with the scope…would love to just send it somewhere and pay a reputable Tek tech to make it right but I’m not sure where to turn for that, so in lieu of that hoping I can get some assistance here.

My AA 501A is fitted with Option 1…I’ll have to test the SG 502 again…there are independent 30kHz and 80kHz LPFs and a 400Hz HPF on mine.

Cory


Eric
 

Cory,
Ill help where I can I have made it a habit to repair a scope or two. Your AA501A is configured exactly the same as mine. You should also have a filter labeled "A weight" this is a fixed tuned curve the A stands for "Audio" It puts some EQ on the input filter. The manual has the exact response curve in it if I remember correctly. It was supposed to be a pleasing response specifically for testing audio gear. To truly do a cal on it if that is you goal you will need a SG505 Option 1 as well. The bread and butter of the AA501 is in the audio listening range, But it is a very capable instrument under 100 Khz. And will the 200 Vac input rating it is definitely less finicky then a spectrum analyzer.

Eric

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of sweetbeats
Sent: Monday, June 21, 2021 5:13 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] SG 502 Assistance?

Thanks again, Eric!

I will be careful with the scope…would love to just send it somewhere and pay a reputable Tek tech to make it right but I’m not sure where to turn for that, so in lieu of that hoping I can get some assistance here.

My AA 501A is fitted with Option 1…I’ll have to test the SG 502 again…there are independent 30kHz and 80kHz LPFs and a 400Hz HPF on mine.

Cory