Here’s a schematic. I’m not a DIY guy I’m simply here to ask the experts and I’d appreciate input.
I have generally found I get the top end I like out of miniature tubes vs the octal or larger tubes and since my 6550 Tung Sols lack that extended highs I want- hoping I can use adapters for the 6BX/L7 drivers. So could a 5687 tube work with an adapter? Any other options? 6CG7?
May as well ask while I’m here. I also have matching transformer coupled preamp which uses 12AY7/6072. Curious if i can safely use a 12AT7 or European equivalent? What about a Western Electric 420a or 396a/5670 via adapters? 5687?
Could the preamp handle a different rectifier other than the 6x4?
Thanks in advance
I have generally found I get the top end I like out of miniature tubes vs the octal or larger tubes and since my 6550 Tung Sols lack that extended highs I want- hoping I can use adapters for the 6BX/L7 drivers. So could a 5687 tube work with an adapter? Any other options? 6CG7?
May as well ask while I’m here. I also have matching transformer coupled preamp which uses 12AY7/6072. Curious if i can safely use a 12AT7 or European equivalent? What about a Western Electric 420a or 396a/5670 via adapters? 5687?
Could the preamp handle a different rectifier other than the 6x4?
Thanks in advance
A 6BX7 is not the driver of my choice. I would use a 12BH7 as a driver or a 12AU7 if you want to use a noval valve.
An EZ80 or EZ81 would suit nicely in the second schematic.
I do hope you are not using the Aircraft Plug for mains, they are only rated for 50volts at 1A. It is not safe.
I presume the twisted double pair is for aesthetics ... not very practical and certainly will not reduce any EMI.
An EZ80 or EZ81 would suit nicely in the second schematic.
I do hope you are not using the Aircraft Plug for mains, they are only rated for 50volts at 1A. It is not safe.
I presume the twisted double pair is for aesthetics ... not very practical and certainly will not reduce any EMI.
If the schematic represents the way your amp is built, then no, you cannot substitute any of those tubes for the 6BX7. The voltages on the schematic would not be at all appropriate for anything except the 6BX7. I wouldn't even sub a 6BL7 in there.
For the preamp, if that is a phono stage I see, then I would not change the 12AY7, since it will mess with the RIAA curve. And I would not mess with the rectifier either.
Both of those pieces are carefully set up around the tubes they use.
For the preamp, if that is a phono stage I see, then I would not change the 12AY7, since it will mess with the RIAA curve. And I would not mess with the rectifier either.
Both of those pieces are carefully set up around the tubes they use.
Wow well I was told 6BL7 would drop right in and I’ve been using it for months and the nos Tung Sol 6BL7 sounded the best of several 6BX7 and 6BL7s so they stayed in. Should I not continue to use it despite nothing wrong these past months?
Unfortunate I can’t use a tube that is more common. I thought with the 5687 being pretty robust and over 12v and often used as a driver in tube amps including in newer amps offered by the same designer- it could work, but that 6BX7 is pretty powerful then?
As for the preamp rectifier I have been using a Bendix 5993 which I was told was a 6x4 in a 9pin tube so I got an adapter for it and it’s been working fine. I was just seeing if there was something else I could use not 6x4 related, but I can live with the Bendix.
Unfortunate I can’t use a tube that is more common. I thought with the 5687 being pretty robust and over 12v and often used as a driver in tube amps including in newer amps offered by the same designer- it could work, but that 6BX7 is pretty powerful then?
As for the preamp rectifier I have been using a Bendix 5993 which I was told was a 6x4 in a 9pin tube so I got an adapter for it and it’s been working fine. I was just seeing if there was something else I could use not 6x4 related, but I can live with the Bendix.
I’m sorry but I have no idea what this means. What is the aircraft plug? The amp is my main amp.
The 6BL7 won't be bothered in that amp but I wouldn't consider it optimal. The problem is that the driver tube is operated with a fixed negative voltage on the grid. At -18 grid volts and 250 plate volts, the 6BX7 is running at a healthy and fairly optimal 40mA per section. The 6BL7 is only running at about 5mA, which means the plate resistance will be much higher, making for a poorer match with the transformer, and the voltage drive will be restricted. But it's not hurting anything. At those same voltages, a 5687 will be barely conducting. Same with the 6CG7. You might get sound but the 6550s will not be driven properly and distortion will be through the roof. Also, the interstage transformer is probably not designed for the much higher plate impedances of those tubes. It's just going to be a mess.
Yes, the 6BX7 is a pretty powerful tube. You can build a modest push-pull power amp with them.
The Bendix isn't hurting anything, assuming it isn't changing the B+ voltage too much.
JonSnell was referring to the connector on that power cord. He's concerned that it's only rated for 50 volts, as opposed to the 100-120 volts used to power the amp. It may look cool but he's concerned about safety.
Yes, the 6BX7 is a pretty powerful tube. You can build a modest push-pull power amp with them.
The Bendix isn't hurting anything, assuming it isn't changing the B+ voltage too much.
JonSnell was referring to the connector on that power cord. He's concerned that it's only rated for 50 volts, as opposed to the 100-120 volts used to power the amp. It may look cool but he's concerned about safety.
Oh, understood. I replaced the connector with a 3 prong iec inlet on both amps already, no ground, however.
I will go back to 6bx7 then even though the Tung Sol 6BL7 clearly has the prettiest highs.
So i suppose the 6550 is strict in it's lack of substitutes as well? I've long been told that i could sub in KT88 was it?
This adapter mentions the Bendix 6384 with adapter can replace 6550s also
https://www.tubedepot.com/products/...jdEYaK5Gxg9ayKbA3pvehL1q_SKCky7u9ejrGBjNDsZJ2
Thanks as well for all the information. Do you have a 6bx7 recommendation? I've used Toshiba. Westinghouse. GE. Sylvania. Raytheon.
I will go back to 6bx7 then even though the Tung Sol 6BL7 clearly has the prettiest highs.
So i suppose the 6550 is strict in it's lack of substitutes as well? I've long been told that i could sub in KT88 was it?
This adapter mentions the Bendix 6384 with adapter can replace 6550s also
https://www.tubedepot.com/products/...jdEYaK5Gxg9ayKbA3pvehL1q_SKCky7u9ejrGBjNDsZJ2
Thanks as well for all the information. Do you have a 6bx7 recommendation? I've used Toshiba. Westinghouse. GE. Sylvania. Raytheon.
Like I said, it won't hurt to use the 6BL7. If it sounds okay, then leave it in. Looking at the schematic, it seems the output tubes have been changed from fixed bias to cathode bias, is that correct? Yes, KT88s are pretty much identical to the 6550. KT66? Maybe, as long as you don't exceed the plate dissipation rating. It looks like they should work provided the amp is cathode bias and not fixed bias. The 6384 has a max screen rating of 325 volts. It might be okay. If you try them and the plates start to glow pink, take them out. I tried Bendix 6889s in my Williamson amps and they were not happy. I have found that Bendix tubes are very sturdy until you start to employ them outside their intended purpose.
I had a gentleman look at it. He said the schematic didn't align exactly. He mentioned fixed. This is the inside. Is that fixed bias?
Bendix tubes would be expensive to try and ruin right away, but i like having rolling options especially with a tube that has NOS options. NOS Tung Sol 6550 are ridiculous prices as well as the winged c's. My NOS GE's are too quiet and failing at this point. The new production 6550s i have sound fine, but kind of veiled and rolled off. 6L6 and KT88 would give me a lot of NOS options to roll.
Bendix tubes would be expensive to try and ruin right away, but i like having rolling options especially with a tube that has NOS options. NOS Tung Sol 6550 are ridiculous prices as well as the winged c's. My NOS GE's are too quiet and failing at this point. The new production 6550s i have sound fine, but kind of veiled and rolled off. 6L6 and KT88 would give me a lot of NOS options to roll.
And this mentions the Bendix 6384 has "The plate rating is 750 volts at 30 watts, which is outrageous for a 6L6 type"
https://www.tubedepot.com/products/...pckUImw-KqtET90TNcjua7k59dhcVD9hxXLydiHjiB9Rx
"When 500v 75 mA was briefly put into the tube, it continued to work without showing red spots on the plate."
https://www.tubedepot.com/products/...pckUImw-KqtET90TNcjua7k59dhcVD9hxXLydiHjiB9Rx
"When 500v 75 mA was briefly put into the tube, it continued to work without showing red spots on the plate."
No, the output tubes are cathode biased, which you can tell by the large white cement resistors and bypass capacitors next to each one. I think KT66's would be fine in that amp. The Gold Lion KT66 is a wonderful tube, the only one I use in my Williamsons. Avoid the Chinese KT66 (sold by TAD, for instance). They sound much worse and produce lower output wattage at higher distortion. You could also try 807s or 5933s with adapter sockets. A very romantic, liquid sound, close to a 300B really. The Gold Lion KT88 is a very good tube. Also, any 6L6GC would be fine. The 7581a is quite a nice tube and relatively inexpensive, has a big open sound. The Tung-Sol reissue 5881 is smooth and buttery and would also work.
The limiting factor with the 6384 is the screen voltage limit, which is 325VDC. Triode-strapped as they would be in this amp, the screens would see 400VDC. They might not be happy. Typically they would have been used as pentodes with lower screen voltages. It's doubtful they would "blow up" but if you try them and notice a red glow at the seams of the plates, I would not continue to use them.
That looks like a nice amp. Can you show us a pic of the top side? Who made it for you? What brand of transformers does it use?
Also, you'd be well off to invest in one of those bias measuring kits. That way you can always check and make sure your output tubes are running within spec. It's a good tool to have, and the math involved is extremely simple:
https://www.tubedepot.com/products/tubedepot-bias-scout-kit
They make fancier ones with built-in meters, but that simple socket and meter would let you check one of the tubes the first time you use them and make sure they are happy.
Also, you'd be well off to invest in one of those bias measuring kits. That way you can always check and make sure your output tubes are running within spec. It's a good tool to have, and the math involved is extremely simple:
https://www.tubedepot.com/products/tubedepot-bias-scout-kit
They make fancier ones with built-in meters, but that simple socket and meter would let you check one of the tubes the first time you use them and make sure they are happy.
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That's some awesome bit of information and exactly what i was looking for. Now i have tons of options it seems. Time to spend some money!
One last question. How much of an effect on the sound would changing those bypass caps to film caps have considering its a transformer coupled amp? Isnt the sound quality mostly from the transformers? Same question for the sandcast resistors and what resistors to replace with?
One last question. How much of an effect on the sound would changing those bypass caps to film caps have considering its a transformer coupled amp? Isnt the sound quality mostly from the transformers? Same question for the sandcast resistors and what resistors to replace with?
Oh, regardless of of transformers, cathode resistors and caps make a difference. I can't quite see what the caps are, maybe 33uF? You could use film caps, but they would be large. A nice upgrade would be Elna Cerafines, AudioNotes or Nichicon Muse electrolytics. For the resistors, Mills 12 watt wirewounds would be nice. If you have a multimeter, I would measure the resistors (with the amp off, of course) before you buy to make sure of the value. All three options are available from Parts Connexion in Canada.
Thanks and yes If I recall correctly it is a 33uf or close to there and it would be a huge capacitor. Could an electrolytic bypassed by a small silver capacitor yield good results?
The amp had a 2 prong connector and cable. I simlpy just had the 2 connected to hot and neutral of the 3 prong iec and didn’t add a ground that was never there. Both amps go to a grounded 100v to 120v isolation transformer and voltage converter from the same designer.
The amp had a 2 prong connector and cable. I simlpy just had the 2 connected to hot and neutral of the 3 prong iec and didn’t add a ground that was never there. Both amps go to a grounded 100v to 120v isolation transformer and voltage converter from the same designer.
See photo.
It is dangerous to use such a connector for mains voltage!
Attachments
Yeah the amps came with that connector and only the power amp had the cable so since i needed to put a normal iec inlet on the preamp, i went ahead and did it to the power amp and now use normal power cables on them both. As mentioned, both amps go into a grounded isolation transformer doubling as a voltage converter for use in 120v. I have the grounded power cable on that one. Yall are saying all my amps should be grounded? Most of my DACS ive ever had through here don't have ground. Should those be grounded as well?