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SAE 2200 Rehab Project - questions

sabrefencer said:
I also have a few questions about the 62ohm bias resistors. I plan on replacing both of them, since one appears to have been replaced and I want them to match. They measure 60.7 and 62.5 ohms (in circuit). I have seen a reference that these are fuseable, but I can’t confirm this and can’t find 62ohm 1/2 W fuseable resistors. I saw the fuseable reference in a 2400 service manual that I have.

I am thinking of using 62ohm 1W, 1% resistors 279-H4P62RFZA, there is a 1/2W H462RBYA which are 0.1% precision which seems like it might be overkill at $2.24 each. But maybe in this application that's appropriate. Typically I wouldn’t hesitate to go from from a 1/2W to 1W resistor, since if they are functioning as a fuse, the higher wattage rating might not be a good idea.

There don't seem to be too many choices in 62 ohm resistors. Is there a go-to for these bias resistors, or will any 1% metal film resistor work fine?
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I go with a metal film, most times PR series from Vishay. 1, 2 or 3 watt depending. Sometimes Ohmite 45 series for “special” spots.
 
sabrefencer said:
I would also like to get your input on transistor selection:

I already have OnSemi MJ21193/94 for the outputs, and MJE15032/33 for the drivers.

For the other TO-220s on the driver board (Q9,10,11,12) I’m looking at KSA940/KSC2073.

For the TO-92s it has been suggested to use MPSA06 and MPSA56. Would these be a good choice to replace all the TO-92’s in the unit? My unit has 2N5210/2N5087 for the 8 limiter transistors, are these the BC transistors you referred to in post #2? Should I use direct replacements for these, and go with the MPSAs for the others on the driver board, and on the output and power supply board?

I think the 2N5210/2N5087 have higher gain than the MPSAs, but I was not able to tell conclusively from the datasheets I read. I do plan on testing the old ones with my Atlas DCA55 meter when I pull them, and compare gain with the new ones, but I want to make sure I order the right ones in the first place.

I do most of my work on tube gear, and I am still a bit hesitant when it comes to selecting replacement transistors. It's just too easy to replace a 12AX7 with a 12AX7, so I'm spoiled.

Any help from you or @llwhtt would be most appreciated,
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Same I use on outputs and drivers. Those other TO220’s I just use the same, MJE15030,1,2 or 3’s if mounted on a heat sink. Starting using CEN07 & 57’s for those S1375/76’s. Those 5210/5087’s should be fine to use. They used different ones as the years went by and availability changed.
 
So what are you trying to do with this amplifier? It sounds like you now are looking at replacing everything.
 
Great question!

The simple answer is yes, I was planning to replace most of it. But your question is making me think again.

My plan was to go through the amp from input to output and replace what needs to be replaced, and maybe go a bit further and do some preemptive replacements, so I don't have to go back in again. Also, the more I work on this amp, the better I will know SAE amps, and will then tackle my 2400L.

I have had this amp for 45 years, and it does have a few known issues. 1) Hum or buzz from the transformer 2) Display has always been flaky and has not worked in a few years 3) The amp smoked in 1981 and there are signs of burned (now replaced) components on the driver board and output board, and the replacements were only done on one channel, 4) After 45 years, I think the electrolytics should be replaced, 5) Preemptive/upgrade replacement of resistors (especially matched pairs) and transistors that do not test well or that could be matched better.

Before I dig into it, I want to have most or all parts on hand, so I don't have too many interruptions waiting for one component to finish a board.

I replaced two caps on the display board -- which is the early type with discrete transistors, not op-amps, and the display now works fine, so #2 is done. That leaves #1, 3, 4, 5 in my list above.

I think the minimum to replace is: Filter caps, small caps on the PS board, opt transistors, and on the driver board: driver transistors, all the electrolytics, and a few resistors that have had or are known to have issues. So my thinking is if I am doing this much, why not be prepared to replace everything that is remotely suspect.

Do you think I am going too far?
 
Oh gosh no. If I have any inclination, I might keep an amp, I go and replace most everything. With these SAE's I have found it simpler in the long run to just do it that way instead of constant trouble shooting for some 0.50 cent part.
I tend to replace all the diodes and 1/2 watt and up resistors too. Power supply I like to replace it all. Relay/protection board replace it all too.
I'm sure plenty of person's think this is stupid but it's what I do, I try not to "push" this on anyone.
 
sabrefencer said:
Great question!

The simple answer is yes, I was planning to replace most of it. But your question is making me think again.

My plan was to go through the amp from input to output and replace what needs to be replaced, and maybe go a bit further and do some preemptive replacements, so I don't have to go back in again. Also, the more I work on this amp, the better I will know SAE amps, and will then tackle my 2400L.

I have had this amp for 45 years, and it does have a few known issues. 1) Hum or buzz from the transformer 2) Display has always been flaky and has not worked in a few years 3) The amp smoked in 1981 and there are signs of burned (now replaced) components on the driver board and output board, and the replacements were only done on one channel, 4) After 45 years, I think the electrolytics should be replaced, 5) Preemptive/upgrade replacement of resistors (especially matched pairs) and transistors that do not test well or that could be matched better.

Before I dig into it, I want to have most or all parts on hand, so I don't have too many interruptions waiting for one component to finish a board.

I replaced two caps on the display board -- which is the early type with discrete transistors, not op-amps, and the display now works fine, so #2 is done. That leaves #1, 3, 4, 5 in my list above.

I think the minimum to replace is: Filter caps, small caps on the PS board, opt transistors, and on the driver board: driver transistors, all the electrolytics, and a few resistors that have had or are known to have issues. So my thinking is if I am doing this much, why not be prepared to replace everything that is remotely suspect.

Do you think I am going too far?
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It's cool to have it from when you originally bought it.
 
OK, it's nice to have the reality check. Yes, all the diodes are on my list, the larger resistors, probably the .1 film caps, and pretty much everything on the PS and output board. The relay seems to be working, so I was not planning on touching it.

I'm very comfortable with doing the work, just don't have enough experience matching currently available transistors to the originals. I find it to be a time consuming process. For the TO 92's I am going to order both the MPSA06/56 and the 2N5210/2N5087 and test the pulls vs replacements with the Atlas DCA55 and put in what makes the most sense. For the TO-220s I have 6 each of MJE15032/33 and will match up pairs for the 2200 and two pairs for the 2400L. These came from Newark in the UK, as neither Mouser or Digikey had both. For the other TO-220s I will also order the KSA940/KSA2073 and check them, and if they are do not seem to be a good match, I will use the MJEs, and get more when I do the 2400.

I've got Nichicon LKG 10000uf 63v filter caps on order, and will use Nichicon UVZ for the small caps on the PS board, and UFG for the driver board. The 3A diodes on the PS board will get UF5402, and the 1N4004s will be replaced with 1N4007. The zener and other small diodes with same spec units. I will get the Piher pots for the bias, and use a 2M Bourns for the select resistor on the driver board.
 
sabrefencer said:
OK, it's nice to have the reality check. Yes, all the diodes are on my list, the larger resistors, probably the .1 film caps, and pretty much everything on the PS and output board. The relay seems to be working, so I was not planning on touching it.

I'm very comfortable with doing the work, just don't have enough experience matching currently available transistors to the originals. I find it to be a time consuming process. For the TO 92's I am going to order both the MPSA06/56 and the 2N5210/2N5087 and test the pulls vs replacements with the Atlas DCA55 and put in what makes the most sense. For the TO-220s I have 6 each of MJE15032/33 and will match up pairs for the 2200 and two pairs for the 2400L. These came from Newark in the UK, as neither Mouser or Digikey had both. For the other TO-220s I will also order the KSA940/KSA2073 and check them, and if they are do not seem to be a good match, I will use the MJEs, and get more when I do the 2400.

I've got Nichicon LKG 10000uf 63v filter caps on order, and will use Nichicon UVZ for the small caps on the PS board, and UFG for the driver board. The 3A diodes on the PS board will get UF5402, and the 1N4004s will be replaced with 1N4007. The zener and other small diodes with same spec units. I will get the Piher pots for the bias, and use a 2M Bourns for the select resistor on the driver board.
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You should be good to go. Matching the Input Differential pairs will help that DC Offset go down.
 
Thanks for your help. I will be putting the order into Mouser soon. When I get into it I will start a new thread documenting my rebuild, and any questions I might have.
Gary
 
hamrules said:
That DC Offset can be lowered if you want by closer matched input differential pairs and/or making sure those high ohm resistors are close matched, the 15k & 150k (180k ?) ones I believe (Looks to be different values depending when built). I assume you have the BC series transistors in those positions? If so real easy to replace and get that down a lot lower.
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From Amazon get a PEAK electronic design ltd ATLAS DCA55 and measure your transistors in the differential input pair and get them to have a hfe as close as possible to each other. Then do your opposing matched sets PNP and NPN pairs for as close a hfe as possible.
 
sabrefencer said:
I have been the owner of an SAE 2200 power amp since 1977. I am preparing to do a full refrurb on this amp. This is an early version (SN below 1000) of the 2200 which had some issues addressed by multiple service bulletins (which I have), and which were fixed on later units by revision of the design. The amp is functioning, with no noticeable audible issues. It was last serviced in the early ‘80s, and this service did not fully/correctly apply the service bulletins. Specifically, the Fairchild output transistors were only changed on the one channel that let out magic smoke in 1981, but the others are still in there and ticking toward their likely demise.

To get a baseline for my work, I did get some “before” measurements of the unit. Visible clipping on the scope was at 30 volts RMS or about 112 watts for both channels driven into 8ohm dummy loads with a 1kHz signal. Distortion at 1kHz measured about 0.2% on both channels at 50 watts. Given the limitations of my HP334A analyzer, these measurements seem fine for a unit that has not seen a tech in 40+ years. They also show that despite the half-way repair, both channels are performing about the same.

DC offset is about 54 mV on both channels, which I think is right at the spec limit.

I measured the bias at the 62 ohm resistors on the driver board, with a 20kHz input signal at 2.8v output to 8ohm dummy loads (1 watt) per SAE service bulletin 2200-01. However, turning the bias pots makes only very small adjustments over a range from about 0.4 vDC to 0.76 vDC, but I can’t get it up near 1v, on either channel. My understanding is that 1.0vDC is the target setting. I measured the resistance of the trim pot that I could get to without removing the output module, and its range is from 1.5 ohms to about 418 ohms, which seems about right for a 500 ohm pot. The 62 ohm resistors read 60.7 and 62.5 ohms (in circuit), which also seems "close enough". Turning the pots also barely moves the needle on the distortion analyzer. Am I measuring this right? Any thoughts on why I can’t get a better range of adjustment?

Do any of the resident SAE 2X00 series gurus such as @llwhtt or @hamrules have any ideas whats going on here?

Gary
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Where can I get those SAE 2200 service bulletins?
Thanks Al Harper
 
Stereomanuals .com has the full SM with schematic and service bulletins. They will send you paper copy. Not free but worth it.
 
I have the 2200 Service Manual with Bulletins, start a conversation with me if you want it.
 
I have a service manual from manualslib.com but it is poor quality hard to read,. However I don't have all the updates if it isn't too much trouble could you send them. I am using a 2400 and 2600 manual as backup inspecting both to make a decision on component to use. I did find using replacement transistors with hfe 100 lower than originals made the 2600 inoperable. It took me a while to get some useful transistors.

I noticed you are a TUBE man! I could use a few questions answered regarding the 1000W amp I am building using 2 pairs of 813 for the push pull output stage. I am new and unsure how or if I can communicate directly or if I open a new thread?
 
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