A guitar amp tech I know of and trust doesn't like the CE caps, Finds they don't last as long as they should, though you get a can cap to keep the look. Many guitar amp techs seem to like the F&T caps though they are axials that you would need to find room for under the chassis.
My 2 cents.
S.
My 2 cents.
S.
How do you know the 7591A is a true power pentode?
I see it being called a power pentode in a RCA datasheet but in the Tung-Sol and Westinghouse datasheets is being called a beam power pentode.
No problem,
Okay, for coupling caps, use axial polypropylene types of any decent brand. There is no sound difference between them, but there are for different dielectric material like polyester. Above all, they must fit properly, hopefully smaller size these days, and the rated voltage must be equal or greater than the full supply voltage before the tubes warm up. The exception are any coupling capacitors coming off the cathode of the tubes. Beyond that it is pretty simple. Beware if someone is totally sold on any one brand of capacitor, especially if it is an expensive "audio brand".
You should measure the plate resistors and replace any out of tolerance. There are many other things I do to improve performance, but I'm not going to go through all of that.
I am not familiar with this person, which is neither good or bad. If his work is neat and looks like how they built it originally you should be fine. If he leaves the original can filter caps in and wires other capacitors in parallel the work was done improperly and you need to have someone else redo the job. Some of the worst techs have glowing referrals, so you can't go by that. His work should look original and neat. Use your eyes on previous work, he should have pictures. If it doesn't look right, it probably isn't.
This is a shot of something I recently did. It wasn't intended to be perfect or super neat, but is an example of what you should expect. This is the phono section in an Eico HF81 preamp.
Okay, for coupling caps, use axial polypropylene types of any decent brand. There is no sound difference between them, but there are for different dielectric material like polyester. Above all, they must fit properly, hopefully smaller size these days, and the rated voltage must be equal or greater than the full supply voltage before the tubes warm up. The exception are any coupling capacitors coming off the cathode of the tubes. Beyond that it is pretty simple. Beware if someone is totally sold on any one brand of capacitor, especially if it is an expensive "audio brand".
You should measure the plate resistors and replace any out of tolerance. There are many other things I do to improve performance, but I'm not going to go through all of that.
I am not familiar with this person, which is neither good or bad. If his work is neat and looks like how they built it originally you should be fine. If he leaves the original can filter caps in and wires other capacitors in parallel the work was done improperly and you need to have someone else redo the job. Some of the worst techs have glowing referrals, so you can't go by that. His work should look original and neat. Use your eyes on previous work, he should have pictures. If it doesn't look right, it probably isn't.
This is a shot of something I recently did. It wasn't intended to be perfect or super neat, but is an example of what you should expect. This is the phono section in an Eico HF81 preamp.
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Hi PFL200,
It might be either I guess, similar to an EL34 or 6CA7. I haven't examined the internals in detail. However, a beam power tube is more efficient and normally has lower plate resistance. If you have a choice, a beam power tube is the way to go.
When looking it up, I didn't see the need to look up multiple data sheets for it. I guess we could do an exhaustive study on it, for what that's worth. But since we are changing the tube type, does it really matter? May as well go for the better tube type.
Hey Steve,
I have not had any problems with CE branded parts and have used them for years. Now, in guitar amplifiers (which I service), conditions are totally different than in reproduction amplifiers. The circuit is normally upside down and heat may pool there. Twist-loc can caps are rarely used in guitar amps as well. So the only only other option for replacement would be stuffing the old can full of new caps - cutting off ventilation and causing premature failure. A terrible plan! I have heard of Hayseed Hamfest only recently, but am nervous about how they make them.
CE branded caps are made on original Mallory machinery, they are high reliability capacitors. I think that if you don't have direct experience with a product, repeating what you heard is probably not helpful. Just saying.
It might be either I guess, similar to an EL34 or 6CA7. I haven't examined the internals in detail. However, a beam power tube is more efficient and normally has lower plate resistance. If you have a choice, a beam power tube is the way to go.
When looking it up, I didn't see the need to look up multiple data sheets for it. I guess we could do an exhaustive study on it, for what that's worth. But since we are changing the tube type, does it really matter? May as well go for the better tube type.
Hey Steve,
I have not had any problems with CE branded parts and have used them for years. Now, in guitar amplifiers (which I service), conditions are totally different than in reproduction amplifiers. The circuit is normally upside down and heat may pool there. Twist-loc can caps are rarely used in guitar amps as well. So the only only other option for replacement would be stuffing the old can full of new caps - cutting off ventilation and causing premature failure. A terrible plan! I have heard of Hayseed Hamfest only recently, but am nervous about how they make them.
CE branded caps are made on original Mallory machinery, they are high reliability capacitors. I think that if you don't have direct experience with a product, repeating what you heard is probably not helpful. Just saying.
Anatech,
Granted, second hand information can be suspect and normally I wouldn't pass it on. But when it comes from someone who for over 20 years has made their living servicing amps for gigging musicians I think it's a valid data point. I'm not denying your experience but when someone won't use a product because it could damage their professional reputation I think their experience is worth considering.
But as far as coupling caps go, I've had good experience using Cornell-Dubilier 940 and 942 series polypropylene caps. They are designed for pulse circuits but have proven themselves in audio applications to my satisfaction. They do cost more than cheap polyester film caps, but no where near what boutique audio caps sell for. They are available from Mouser, when they have stock (like everything else recently).
S.
Granted, second hand information can be suspect and normally I wouldn't pass it on. But when it comes from someone who for over 20 years has made their living servicing amps for gigging musicians I think it's a valid data point. I'm not denying your experience but when someone won't use a product because it could damage their professional reputation I think their experience is worth considering.
But as far as coupling caps go, I've had good experience using Cornell-Dubilier 940 and 942 series polypropylene caps. They are designed for pulse circuits but have proven themselves in audio applications to my satisfaction. They do cost more than cheap polyester film caps, but no where near what boutique audio caps sell for. They are available from Mouser, when they have stock (like everything else recently).
S.
Hi Steve,
Yes, polypropylene are about the best in the higher values of capacitance. I didn't look up those series of caps you lised, but I will only say that you should never use a radial capacitor where an axial leaded part went where the radial leads will make the capacitor sit in a different spot. (ie orange drops where axial leaded parts were).
I was only pointing out that the application and conditions were different between guitar amplifiers and home audio amplifiers. You can't really "read across". Same for tube shoot-outs, totally different conditions and goals. The data point is only valid where conditions are the same. Otherwise all bets are off. Only the person with direct experience knows what may be different between the two situations. Notice I am not saying he is wrong.
Guitar amps are normally built as inexpensively as possible for the power output. As such, they normally use either axial leaded filter caps, or more recently radial or snap mount caps. A Twist-loc cap is typically found in industrial or consumer equipment as they cost a lot more. They always did. I once worked at a parts jobber and sold parts to industry and consumer / MI clients. I did make it my business to learn about the parts I was selling to better serve our customers.
Yes, polypropylene are about the best in the higher values of capacitance. I didn't look up those series of caps you lised, but I will only say that you should never use a radial capacitor where an axial leaded part went where the radial leads will make the capacitor sit in a different spot. (ie orange drops where axial leaded parts were).
I was only pointing out that the application and conditions were different between guitar amplifiers and home audio amplifiers. You can't really "read across". Same for tube shoot-outs, totally different conditions and goals. The data point is only valid where conditions are the same. Otherwise all bets are off. Only the person with direct experience knows what may be different between the two situations. Notice I am not saying he is wrong.
Guitar amps are normally built as inexpensively as possible for the power output. As such, they normally use either axial leaded filter caps, or more recently radial or snap mount caps. A Twist-loc cap is typically found in industrial or consumer equipment as they cost a lot more. They always did. I once worked at a parts jobber and sold parts to industry and consumer / MI clients. I did make it my business to learn about the parts I was selling to better serve our customers.