It can seem that way, but tube circuits are some of the first and simplest of electrical circuits
This may help:
http://www.allaboutcircuits.com/
The NEETS training mentioned above is also at
http://www.tpub.com/neets/
from
http://www.tpub.com/
jmillerdoc: Do the mods, it's worth it, and cost effective, and you'll probably learn something along the way. Keep in mind that tubes use high voltage so respect that when repairing/troubleshooting.
The Low ESR panasonic electrolytic caps that grhughes mentioned are great replacement caps for HV psu caps. They are Panasonic TS-HA TS-HB, or ED series. The HA's are rated up to 400V, the HB's are rated up to 450V. IIRC, the ED's are rated up to 400 and have radial leads instead of snap-in leads. These are available from Digi-key and elsewhere, but not Mouser IIRC.
The Orange drop 716P caps are inexpensive (like $1.50/ea) and are a great bang-for-the-buck cap for the small value high voltage caps. I believe either Mouser or Digikey sells them but I could not find them in a quick search I just did.
When replacing caps, shoot for the same capacitance value and a voltage rating the same or greater than the original part. Higher voltage rated parts are physically larger, so make sure you'll have the real estate to fit them in. Most electrolytics are toleranced rather loosely (+/- 20%) so sometimes replacement parts are not available in the original values. If you get a replacement cap within 20% of the original, you should be fine, or you can parallel two caps together to get to the required uf.
It also sounds like you have some caps that are multiple caps in single cans. JJ electronics (and others) make HV caps that are multiple uf's in one can. The tube depot and the tube store (among others) sell these. Here is a link:
http://www.tubedepot.com/can.html
Replacing the old carbon comp resistors with more modern metal films as grhughes mentioned is another worthwhile mod, although some folks like the "vintage" sound of the carbon comps. I can post a pic of the typical carbon comp R vs metal film R so that you can identify them easily if you are not familiar with the difference.
I am not familiar with your particular unit; it sounds like you have some obsolete inputs according to Eli. In general, (your unit sounds like an exception here) most preamp (and integrated amp) inputs are all "line level" inputs except for the phono input, which has higher gain than the others and some equalization (RIAA phono equalization). So in general, Tape, Aux, CD, etc are all equivalent inputs and are all line level inputs.
The Low ESR panasonic electrolytic caps that grhughes mentioned are great replacement caps for HV psu caps. They are Panasonic TS-HA TS-HB, or ED series. The HA's are rated up to 400V, the HB's are rated up to 450V. IIRC, the ED's are rated up to 400 and have radial leads instead of snap-in leads. These are available from Digi-key and elsewhere, but not Mouser IIRC.
The Orange drop 716P caps are inexpensive (like $1.50/ea) and are a great bang-for-the-buck cap for the small value high voltage caps. I believe either Mouser or Digikey sells them but I could not find them in a quick search I just did.
When replacing caps, shoot for the same capacitance value and a voltage rating the same or greater than the original part. Higher voltage rated parts are physically larger, so make sure you'll have the real estate to fit them in. Most electrolytics are toleranced rather loosely (+/- 20%) so sometimes replacement parts are not available in the original values. If you get a replacement cap within 20% of the original, you should be fine, or you can parallel two caps together to get to the required uf.
It also sounds like you have some caps that are multiple caps in single cans. JJ electronics (and others) make HV caps that are multiple uf's in one can. The tube depot and the tube store (among others) sell these. Here is a link:
http://www.tubedepot.com/can.html
Replacing the old carbon comp resistors with more modern metal films as grhughes mentioned is another worthwhile mod, although some folks like the "vintage" sound of the carbon comps. I can post a pic of the typical carbon comp R vs metal film R so that you can identify them easily if you are not familiar with the difference.
I am not familiar with your particular unit; it sounds like you have some obsolete inputs according to Eli. In general, (your unit sounds like an exception here) most preamp (and integrated amp) inputs are all "line level" inputs except for the phono input, which has higher gain than the others and some equalization (RIAA phono equalization). So in general, Tape, Aux, CD, etc are all equivalent inputs and are all line level inputs.
an oth,ver link <http://www.r-type.org/static/hi-fi.htm>
ps... i like to smash the window any how .....what the hell?
ps... i like to smash the window any how .....what the hell?
More, More, More
Ok, I've slept since last post! I am freash and now more willing to comprehend all this stuff.
1) Since yesterday I have disassembled parts of the amp, mostly just the service cowlings.
2) bought some electrical contact cleaner and sprayed out all the moving electrical parts (knobs, swicthes). Operates now without a single scratch , snap, or pop when moving the knobs or switches.
3) the far left 7189 is glowing again. Tried to wriggle it but still glows. Immediately turned amp off.
4) Noticed all the tubes are Telefunken except one of the 7189's is a GE as well as the rectifier.
5) moved the GE 7189 to the far left position so when turned on it won't screw up the Telefunkin!
6) GE 7189 in the far left position glows there too.
7) Found a guy in Lawton, OK who services Tube amps. He comes highly reccommended around these parts. Took the amp to him toady for a 25.00 bench fee to tell me exactly whats wrong with it since I lack much of the equipment you guys must have. He will give me a list of problems and parts for what he finds then I will post it here tomorrow. See what you all think.
8) Think I can find a matching 7189 NOS Telefunkin out there to go with my other 3 if they are all ok? How much should one cost if I find one? Do any of y'all have one?
9) to reiterate, in the current state the amp does not hum at all! not even a hint. The right side sounds weaker than the left, esp the mids and bass, but bass is sloppy on both sides. The lower treble to the high highs is superb sounding!
!0) I pulled the bottom cover off and everything on thorough inspection is clean and new looking for a 51 year old amp. Noticed several white 1/2in by 2in (appx) white capacitors with values ranging from .1, .22, .47, .0083, and others I'm sure. Are these elecrtrolytic? They look very similar to a Bennic poly cap. Are these the ones I should completely replace. They all look good. They all look easy to replace.
11) on the topside of the amp, to the right of the 6BL8 and 7189 and just to the left and a bit back from the main transformer are x3 tall white cylindrical "porcelin" looking 1/2 to 5/8 in diameter and 2.5 to 3 in tall objects that on the top have a "cement" looking substance filling them. they get very hot too. What are these? Resistors?
Nurse calling, gotta go, much more to come later!!!
Thanks to all,
Jeff Miller
Lawton, OK
Ok, I've slept since last post! I am freash and now more willing to comprehend all this stuff.
1) Since yesterday I have disassembled parts of the amp, mostly just the service cowlings.
2) bought some electrical contact cleaner and sprayed out all the moving electrical parts (knobs, swicthes). Operates now without a single scratch , snap, or pop when moving the knobs or switches.
3) the far left 7189 is glowing again. Tried to wriggle it but still glows. Immediately turned amp off.
4) Noticed all the tubes are Telefunken except one of the 7189's is a GE as well as the rectifier.
5) moved the GE 7189 to the far left position so when turned on it won't screw up the Telefunkin!
6) GE 7189 in the far left position glows there too.
7) Found a guy in Lawton, OK who services Tube amps. He comes highly reccommended around these parts. Took the amp to him toady for a 25.00 bench fee to tell me exactly whats wrong with it since I lack much of the equipment you guys must have. He will give me a list of problems and parts for what he finds then I will post it here tomorrow. See what you all think.
8) Think I can find a matching 7189 NOS Telefunkin out there to go with my other 3 if they are all ok? How much should one cost if I find one? Do any of y'all have one?
9) to reiterate, in the current state the amp does not hum at all! not even a hint. The right side sounds weaker than the left, esp the mids and bass, but bass is sloppy on both sides. The lower treble to the high highs is superb sounding!
!0) I pulled the bottom cover off and everything on thorough inspection is clean and new looking for a 51 year old amp. Noticed several white 1/2in by 2in (appx) white capacitors with values ranging from .1, .22, .47, .0083, and others I'm sure. Are these elecrtrolytic? They look very similar to a Bennic poly cap. Are these the ones I should completely replace. They all look good. They all look easy to replace.
11) on the topside of the amp, to the right of the 6BL8 and 7189 and just to the left and a bit back from the main transformer are x3 tall white cylindrical "porcelin" looking 1/2 to 5/8 in diameter and 2.5 to 3 in tall objects that on the top have a "cement" looking substance filling them. they get very hot too. What are these? Resistors?
Nurse calling, gotta go, much more to come later!!!
Thanks to all,
Jeff Miller
Lawton, OK
Your amp requires a WELL matched pair of tubes in each channel. NOS TFK and Mullard made power O/P types are scarcer than hen's teeth. If you can find them, the price includes some of your vital organs.
Buy 2 matched pairs of the "Ruskies" I previously mentioned from McShane. Test the tubes you already have. If they are reasonably strong, the TFK 7189s will be worth some money.Those are probably waxed paper dielectric. Replacing with 716P series "Orange Drops" is probably in order. Definitely replace the coupling caps. between splitters and "finals". Tighten the sockets up too. BTW, if you see a cap. that looks like a small domino, it's mica. Given your mention of Bennic, you probably know what a ceramic disk cap. looks like.
Yes, those are wirewound power resistors. Surprise (not), the Laws of Ohm and Kirchoff hold true, regardless of technology type. I2R heating is a fact of life.
Properly matched O/P tube pairs and replacement of the NFB gain set resistors, along with correct setting of the 3 trim pots., should bring the 2 channels into line. Tube amps (even those employing loop NFB, like the 299B) simply don't have the damping factor "sand" amps have. The 299B should be mated to speakers of at least 90 dB. sensitivity. Also, those speakers should have a reasonably flat impedance curve.
Telefunkin 7189
I am having my telefunkin 7189's tested as we speak. If they test good they will be for sale!!! Wonder how much I could get for three good ones? Maybe enough to buy all of the other parts needed! I don't think I'm that lucky. Well then, how oftrn does a friend call you up and ask you if you want a perfect (looking) vintage tube amp! Maybe I will be that lucky.
I am having my telefunkin 7189's tested as we speak. If they test good they will be for sale!!! Wonder how much I could get for three good ones? Maybe enough to buy all of the other parts needed! I don't think I'm that lucky. Well then, how oftrn does a friend call you up and ask you if you want a perfect (looking) vintage tube amp! Maybe I will be that lucky.
Some answers
white capacitors with values ranging from .1, .22, .47, .0083, and others I'm sure. Are these elecrtrolytic?
Those capacitors are all small value caps and can be replaced with the SBC 716P metalized polypropylene caps. These caps are greatly responsible for the sonic signature of the amp. No they are not electrolytic. Electrolytics are polarized like batteries and they are reservoirs to store DC. They will have clear polarity markings + and -. an + anode and a - cathode and most are above 5 ufd.
The ceramic standups on top of the chassis are ceramic resistors. They are up top to be ventilated. These seldom give problems.
I take it that this is an adjustable bias amp meaning the amp's output stage runs in a mode called "fixed bias" in which a negative DC voltage from a separate negative power supply is applied to the grids. If it had no bias adjustment then it's output stage would run in a mode called "cathode bias" in which the tubes make their own bias (there would be no bias pot and no seperate negative power supply). TUBES AGE! Their cathode eventually sheds all it's coating. It's burned off. As it's burned off the tube's emission declines and so does it's transconductance. The chances of you finding another Telefunken 7189 to match those that are aged is slim to none. You would have to have about 25 Telefunken7189s and go through them on a mu (mutual transconductance) tube tester to find which matches. Best to replace all the output tubes with four new MATCHED tubes. You can easily buy new matched tubes from a number of suppliers. There are also numerous tubes of different number that will work with minor re-wiring but then that would make your Scott MODIFIED.
Hiring a qualified technician is a good idea. If he is worth his salt, then he will test all the tubes, make a log of each one as to it's mu-transconductance and recommend those that need replacement. You will then have a good sounding amplifier.
Tube amps typically have superior midrange and treble. That's where they shine! Their bass is not as good as a solid stage amp because of damping factor that is lost in inductance in the output transformer. Ray
white capacitors with values ranging from .1, .22, .47, .0083, and others I'm sure. Are these elecrtrolytic?
Those capacitors are all small value caps and can be replaced with the SBC 716P metalized polypropylene caps. These caps are greatly responsible for the sonic signature of the amp. No they are not electrolytic. Electrolytics are polarized like batteries and they are reservoirs to store DC. They will have clear polarity markings + and -. an + anode and a - cathode and most are above 5 ufd.
The ceramic standups on top of the chassis are ceramic resistors. They are up top to be ventilated. These seldom give problems.
I take it that this is an adjustable bias amp meaning the amp's output stage runs in a mode called "fixed bias" in which a negative DC voltage from a separate negative power supply is applied to the grids. If it had no bias adjustment then it's output stage would run in a mode called "cathode bias" in which the tubes make their own bias (there would be no bias pot and no seperate negative power supply). TUBES AGE! Their cathode eventually sheds all it's coating. It's burned off. As it's burned off the tube's emission declines and so does it's transconductance. The chances of you finding another Telefunken 7189 to match those that are aged is slim to none. You would have to have about 25 Telefunken7189s and go through them on a mu (mutual transconductance) tube tester to find which matches. Best to replace all the output tubes with four new MATCHED tubes. You can easily buy new matched tubes from a number of suppliers. There are also numerous tubes of different number that will work with minor re-wiring but then that would make your Scott MODIFIED.
Hiring a qualified technician is a good idea. If he is worth his salt, then he will test all the tubes, make a log of each one as to it's mu-transconductance and recommend those that need replacement. You will then have a good sounding amplifier.
Tube amps typically have superior midrange and treble. That's where they shine! Their bass is not as good as a solid stage amp because of damping factor that is lost in inductance in the output transformer. Ray
Jeff,
Earlier in this thread you mentioned only CDP as a signal source. Yes, you can forego replacing the source selector switch and connect to the AUX I/Ps. I still advise you make the change. The Lorlin part I recommended costs less than 5 bucks.
You are getting involved in a lifetime hobby. I'll be turning 64 soon. I built my 1st crystal radio at age 8. You are already "infected". Enjoy the ride!
Earlier in this thread you mentioned only CDP as a signal source. Yes, you can forego replacing the source selector switch and connect to the AUX I/Ps. I still advise you make the change. The Lorlin part I recommended costs less than 5 bucks.
You are getting involved in a lifetime hobby. I'll be turning 64 soon. I built my 1st crystal radio at age 8. You are already "infected".
Enjoy the ride!Re: Some answers
Just a warning - the glow in the one 7189 is not caused by difference in Gm (transconductance). It is caused by excess current passing through the tube.
With amps like yours the key to matching is to have not only Gm match, but matched cathode current. Since you cannot adjust the bias of each individual tube it's imperative that they are well current matched - a mismatch can create a situation where one tube could be loafing (passing a small current) and the other could be fiery red from having to pass too much current. You need tubes that behave pretty much identically under the same set of conditions.
And only a very few tube testers apply a high enough voltage to the tube to do a good job of current matching. I use a special match rig I built, it alows me to run tubes up to 540 volts and 200 ma. I match 7189/EL84M tubes at 330 volts on the plate and screen, much more like the real world.
In general, an amp the age of yours is in need of replacement of a number of components that have long passed the end of their design life. Power supply parts, coupling and bypass capacitors, etc., all need to be replaced. Tube sockets need to be cleaned or replaced if they don't grip the tube pins tightly and securely. And so on...
Vintage tube gear like your Scott is wonderful to own - but it's not "plug and play"!
grhughes said:
Just a warning - the glow in the one 7189 is not caused by difference in Gm (transconductance). It is caused by excess current passing through the tube.
With amps like yours the key to matching is to have not only Gm match, but matched cathode current. Since you cannot adjust the bias of each individual tube it's imperative that they are well current matched - a mismatch can create a situation where one tube could be loafing (passing a small current) and the other could be fiery red from having to pass too much current. You need tubes that behave pretty much identically under the same set of conditions.
And only a very few tube testers apply a high enough voltage to the tube to do a good job of current matching. I use a special match rig I built, it alows me to run tubes up to 540 volts and 200 ma. I match 7189/EL84M tubes at 330 volts on the plate and screen, much more like the real world.
In general, an amp the age of yours is in need of replacement of a number of components that have long passed the end of their design life. Power supply parts, coupling and bypass capacitors, etc., all need to be replaced. Tube sockets need to be cleaned or replaced if they don't grip the tube pins tightly and securely. And so on...
Vintage tube gear like your Scott is wonderful to own - but it's not "plug and play"!
Eli and the bunch pretty much covered it.
The best thing to do is go to Rat shack or go on ebay and find a nice used auto ranging fluke multimeter..Get a good meter tho because you are working with high voltages and impedances many times so accuracy is a premium when reading small cathode voltages.
Like GR says,dont get sucked into expensive botique caps and he is right..A film and foil is a film and foil and they all sound pretty close as I have all of them from Hovlands to auricaps.
If you decide you want better coupling caps for very little money.you buy the surplus Russian k40 paper in oil caps or the Russian ft2 and ft3 teflons..All of these caps will best anything you can buy today IMHO because you have to understand they were made for the Russian Military with Mil Specs and now we can get them for reasonable prices even from Jim McShane.
Also as GR said ,the 105 degree panasonic and nichon caps are what I use even in my most expensive amps and preamps and they sound as good as black gates and even test better in the circuit.
The best thing to do is go to Rat shack or go on ebay and find a nice used auto ranging fluke multimeter..Get a good meter tho because you are working with high voltages and impedances many times so accuracy is a premium when reading small cathode voltages.
Like GR says,dont get sucked into expensive botique caps and he is right..A film and foil is a film and foil and they all sound pretty close as I have all of them from Hovlands to auricaps.
If you decide you want better coupling caps for very little money.you buy the surplus Russian k40 paper in oil caps or the Russian ft2 and ft3 teflons..All of these caps will best anything you can buy today IMHO because you have to understand they were made for the Russian Military with Mil Specs and now we can get them for reasonable prices even from Jim McShane.
Also as GR said ,the 105 degree panasonic and nichon caps are what I use even in my most expensive amps and preamps and they sound as good as black gates and even test better in the circuit.
Folks,
I definitely second the opinions on not to get sucked into the boutique caps. What matters is which dielectric is used in the cap - specifically, the dielectric losses, and absorption. I find that the polypropylene caps have the best characteristics. The "orange drops" people are talking about are polypropylene caps made by Spraque. They're fine caps. Wima makes some fine ones too. You can find more on Digikey.
For power supply caps, you might find that the original values are difficult to obtain. Usually, there's no harm done in using the next standard size up. I.e. if the OEM cap is 180 uF, use a 220 uF (standard value). Similarly for the working voltage (in many cases abbreviated to WV). Note that the new electrolytic caps will likely have much lower Resr (equivalent series resistance), thus, the ripple current will be higher. You might consider (read: I would recommend) replacing the rectifier with a modern silicon version.
First and foremost: Make sure all capacitors are discharged before you start messing with the amplifier. Caps can store charge for quite a while after you turn the amplifier off. Best case, you're in for a nasty surprise and get a mild electric chock. Worst case, you die...!! So be careful.
Tom
I definitely second the opinions on not to get sucked into the boutique caps. What matters is which dielectric is used in the cap - specifically, the dielectric losses, and absorption. I find that the polypropylene caps have the best characteristics. The "orange drops" people are talking about are polypropylene caps made by Spraque. They're fine caps. Wima makes some fine ones too. You can find more on Digikey.
For power supply caps, you might find that the original values are difficult to obtain. Usually, there's no harm done in using the next standard size up. I.e. if the OEM cap is 180 uF, use a 220 uF (standard value). Similarly for the working voltage (in many cases abbreviated to WV). Note that the new electrolytic caps will likely have much lower Resr (equivalent series resistance), thus, the ripple current will be higher. You might consider (read: I would recommend) replacing the rectifier with a modern silicon version.
First and foremost: Make sure all capacitors are discharged before you start messing with the amplifier. Caps can store charge for quite a while after you turn the amplifier off. Best case, you're in for a nasty surprise and get a mild electric chock. Worst case, you die...!! So be careful.
Tom
Moving forward
Ok,
I have spoken with Jim and he has prepared a list of parts generally needed to upgrade the amp to modern specs. I will be getting all these items soon I suspect. For now I will not be replacing the dial. Maybe later. I really appreciate all of the advice. I am miles ahead now because of all of you. Thanks. As soon as I get the parts in and I start working on it I am sure I will be right here asking a zillion more questions! Thanks again!
sincerely,
ADDICTED
Lawton, OK
Ok,
I have spoken with Jim and he has prepared a list of parts generally needed to upgrade the amp to modern specs. I will be getting all these items soon I suspect. For now I will not be replacing the dial. Maybe later. I really appreciate all of the advice. I am miles ahead now because of all of you. Thanks. As soon as I get the parts in and I start working on it I am sure I will be right here asking a zillion more questions! Thanks again!
sincerely,
ADDICTED
Lawton, OK
trying to find Jim
Hi,
It has been a while since I have posted here. I have learned quite alot about tubes since I started here. I was reasing back through the post and I am really grateful you guys didn't laugh at how little I knew. Since I have written last I have completed my Scott 299B project, built 3 tube preamps, and now I am starting on a Scott 222C project. I have since lost Jim McShane's email and I need to get in touch with him. I still have a bag of tubes I need to send him and I need to by 4 more Russian 7189 tubes. Jim, if your'e there, please drop me a line at millerjeff@ccmhonline.com
Thanks everyone,
Jeff
Hi,
It has been a while since I have posted here. I have learned quite alot about tubes since I started here. I was reasing back through the post and I am really grateful you guys didn't laugh at how little I knew. Since I have written last I have completed my Scott 299B project, built 3 tube preamps, and now I am starting on a Scott 222C project. I have since lost Jim McShane's email and I need to get in touch with him. I still have a bag of tubes I need to send him and I need to by 4 more Russian 7189 tubes. Jim, if your'e there, please drop me a line at millerjeff@ccmhonline.com
Thanks everyone,
Jeff
Jeff,
You've got email. Jim McShane is an awesome guy. I've been working on rebuilding an old Packard Bell tube amp and Jim and Eli Duttman have been invaluable. I know the "overwhelming" feeling you mentioned in one of your earlier posts. Judging by the projects you've completed, it looks like you've gotten hooked. Cool stuff!!
Best Wishes,
Mike
You've got email. Jim McShane is an awesome guy. I've been working on rebuilding an old Packard Bell tube amp and Jim and Eli Duttman have been invaluable. I know the "overwhelming" feeling you mentioned in one of your earlier posts. Judging by the projects you've completed, it looks like you've gotten hooked. Cool stuff!!
Best Wishes,
Mike
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