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My very first tube amplifier. Excited!
- Thread starter topgun
- Start date
topgun
Active Member
I’m reading about the EH-6CA7’s you mentioned. Looks like they are interchangeable with the EL34’s. So can those be used without any modifications? If so, I’ll add them to my notes.
if you are talking about the fat bottles, they have a different plate structure than an EL34. Still interchangeable with EL34, but the plates look more like a shunk down 6550 than an EL34. They are pretty robust tubes though. I have gotten a lot of life out of 4 quad sets.
yeah beam tetrodes have a different shape. Completely different internal construction, but electrically interchangeable. Kind of cool really.
I haven't tried them specifically in an ST-70 but I find the 6CA7 to be a little brighter than the EL34 tubes in my two EL34 family amps. Good or bad depending on your ears and speakers. I run a set of the EH 6CA7 in my Pilot SA-260 which is a little challenged on the top end. I run Shugang EL34 tubes which are a little soft on the top end in my Rauland-Borg amps which are on the bright side. Helps balance them both out. The JJ tubes sound like the Mullards, and are right between the EH 6CA7 and the Shugang. Perfectly fine tubes, but they don't really tame the bright amp or the not-so-bright amp so they don't really get much run time.
An ST-70 has more top end than my Pilot does. I had a stock one here for repair a few years ago. I did not roll tubes in it since it wasn't mine and I only had it for a limited window, but just running it with the EH EL34 it came with it was pretty clear. I don't really know that it would benefit from tubes with more top end extension, but thats my ears, my speakers, my room, and a stock circuit amp with 7199 to 6U8 converters in it. All opinions are worth what you paid for them
I really ought to own an ST-70. I don't dislike them, I just don't need one and I don't feel any desire to pay the money they sell for to buy an amp that fills no needs for me. I just know it would end up sitting next to the Pilot SA-260 that doesn't get a lot of use.
I haven't tried them specifically in an ST-70 but I find the 6CA7 to be a little brighter than the EL34 tubes in my two EL34 family amps. Good or bad depending on your ears and speakers. I run a set of the EH 6CA7 in my Pilot SA-260 which is a little challenged on the top end. I run Shugang EL34 tubes which are a little soft on the top end in my Rauland-Borg amps which are on the bright side. Helps balance them both out. The JJ tubes sound like the Mullards, and are right between the EH 6CA7 and the Shugang. Perfectly fine tubes, but they don't really tame the bright amp or the not-so-bright amp so they don't really get much run time.
An ST-70 has more top end than my Pilot does. I had a stock one here for repair a few years ago. I did not roll tubes in it since it wasn't mine and I only had it for a limited window, but just running it with the EH EL34 it came with it was pretty clear. I don't really know that it would benefit from tubes with more top end extension, but thats my ears, my speakers, my room, and a stock circuit amp with 7199 to 6U8 converters in it. All opinions are worth what you paid for them
I really ought to own an ST-70. I don't dislike them, I just don't need one and I don't feel any desire to pay the money they sell for to buy an amp that fills no needs for me. I just know it would end up sitting next to the Pilot SA-260 that doesn't get a lot of use.
topgun
Active Member
I really appreciate all the support you folks have provided me with so far on my first tube project. But unfortunately for me, I have to to put this project on hold until I return from a trip to the Midwest. We are driving from here in eastern Pennsylvania to Oklahoma in a couple of weeks and we will not be back until the middle of November. So it will probably be in early December that I will be able to restart this project and figure out how to get this thing finally up and running so that maybe then I can hear what all the hype about tube amplification is all about. I’ll be back!
topgun
Active Member
Hello everyone,
It’s been a bit since my last update on this project of mine. And since then I’ve replaced the four output tubes with a matched set of JJ EL34ll from the tube store and now I’m able to bias both channels as before I wasn’t able to do so due to a weak or just bad output tube. After that while just using my phone, I plugged it into the input jacks looking for output at the speakers. Except for a very faint hum from both channels, it seems to be working fine.
I then set it aside and decided that I needed to get a hold of a pre-amp to pair with the amp and the logical choice for me was the PAS3x. I good lucky a found one that was like the ST-70, original and unrestored. So I went to work and did all the usual stuff that most people do, I reworked the power supply and added a fuse and a turn on relay for the two switched outlets in the back of the unit. I did not recap the pre amp yet but I did replace the two capacitors coming off the tone controls.
Once I was satisfied that I hadn’t screwed anything up in either unit, I then decided it was time to give them a go so then I can at long last hear what all the fuss is about tube audio.
I hooked everything up and with my fingers crossed I slid the power switch on the PAS to the power position and it all came to life. I must admit I was a little nervous and excited at the same time. Anyways. I wasn’t sure I was impressed initially as I was using a pair heathkit as37 speakers that I have on my bench that sound ok but nothing at all special. I wasn’t ready to hook this thing up to my AR3a’s yet. So as I listened to some classic eagles music, I sat down and gave it a long listen while watching the bias and line voltage, trying to maintain a consistent 117 volts using a variac.
As I continued to listen. It was clear to me that it does indeed sound different than solid state. Once I adjusted the tone controls. I left it alone and listened to the entire disc 1 of the Eagles best of and I now must say I really do enjoy listening to this thing. Even with these unremarkable speakers I was really enjoying myself. Maybe I’m just stroking myself but, I do know the sound is different.
I will listen to it for a couple more days like this and then give it a whirl with the AR’s. I’m expecting a really big difference than with my puny Bench speakers.
I’ll be back. But in the meantime, here are a few pictures of mostly what I did to the PAS3x.
It’s been a bit since my last update on this project of mine. And since then I’ve replaced the four output tubes with a matched set of JJ EL34ll from the tube store and now I’m able to bias both channels as before I wasn’t able to do so due to a weak or just bad output tube. After that while just using my phone, I plugged it into the input jacks looking for output at the speakers. Except for a very faint hum from both channels, it seems to be working fine.
I then set it aside and decided that I needed to get a hold of a pre-amp to pair with the amp and the logical choice for me was the PAS3x. I good lucky a found one that was like the ST-70, original and unrestored. So I went to work and did all the usual stuff that most people do, I reworked the power supply and added a fuse and a turn on relay for the two switched outlets in the back of the unit. I did not recap the pre amp yet but I did replace the two capacitors coming off the tone controls.
Once I was satisfied that I hadn’t screwed anything up in either unit, I then decided it was time to give them a go so then I can at long last hear what all the fuss is about tube audio.
I hooked everything up and with my fingers crossed I slid the power switch on the PAS to the power position and it all came to life. I must admit I was a little nervous and excited at the same time. Anyways. I wasn’t sure I was impressed initially as I was using a pair heathkit as37 speakers that I have on my bench that sound ok but nothing at all special. I wasn’t ready to hook this thing up to my AR3a’s yet. So as I listened to some classic eagles music, I sat down and gave it a long listen while watching the bias and line voltage, trying to maintain a consistent 117 volts using a variac.
As I continued to listen. It was clear to me that it does indeed sound different than solid state. Once I adjusted the tone controls. I left it alone and listened to the entire disc 1 of the Eagles best of and I now must say I really do enjoy listening to this thing. Even with these unremarkable speakers I was really enjoying myself. Maybe I’m just stroking myself but, I do know the sound is different.
I will listen to it for a couple more days like this and then give it a whirl with the AR’s. I’m expecting a really big difference than with my puny Bench speakers.
I’ll be back. But in the meantime, here are a few pictures of mostly what I did to the PAS3x.
Thanks for the follow-up. Enjoy the amp!
topgun
Active Member
Hello everyone,
It’s been a bit since my last update on this project of mine. And since then I’ve replaced the four output tubes with a matched set of JJ EL34ll from the tube store and now I’m able to bias both channels as before I wasn’t able to do so due to a weak or just bad output tube. After that while just using my phone, I plugged it into the input jacks looking for output at the speakers. Except for a very faint hum from both channels, it seems to be working fine.
I then set it aside and decided that I needed to get a hold of a pre-amp to pair with the amp and the logical choice for me was the PAS3x. I good lucky a found one that was like the ST-70, original and unrestored. So I went to work and did all the usual stuff that most people do, I reworked the power supply and added a fuse and a turn on relay for the two switched outlets in the back of the unit. I did not recap the pre amp yet but I did replace the two capacitors coming off the tone controls.
Once I was satisfied that I hadn’t screwed anything up in either unit, I then decided it was time to give them a go so then I can at long last hear what all the fuss is about tube audio.
I hooked everything up and with my fingers crossed I slid the power switch on the PAS to the power position and it all came to life. I must admit I was a little nervous and excited at the same time. Anyways. I wasn’t sure I was impressed initially as I was using a pair heathkit as37 speakers that I have on my bench that sound ok but nothing at all special. I wasn’t ready to hook this thing up to my AR3a’s yet. So as I listened to some classic eagles music, I sat down and gave it a long listen while watching the bias and line voltage, trying to maintain a consistent 117 volts using a variac.
As I continued to listen. It was clear to me that it does indeed sound different than solid state. Once I adjusted the tone controls. I left it alone and listened to the entire disc 1 of the Eagles best of and I now must say I really do enjoy listening to this thing. Even with these unremarkable speakers I was really enjoying myself. Maybe I’m just stroking myself but, I do know the sound is different.
I will listen to it for a couple more days like this and then give it a whirl with the AR’s. I’m expecting a really big difference than with my puny Bench speakers.
I’ll be back. But in the meantime, here are a few pictures of mostly what I did to the PAS3x.
This is what it looked like when it arrived.
It’s been a bit since my last update on this project of mine. And since then I’ve replaced the four output tubes with a matched set of JJ EL34ll from the tube store and now I’m able to bias both channels as before I wasn’t able to do so due to a weak or just bad output tube. After that while just using my phone, I plugged it into the input jacks looking for output at the speakers. Except for a very faint hum from both channels, it seems to be working fine.
I then set it aside and decided that I needed to get a hold of a pre-amp to pair with the amp and the logical choice for me was the PAS3x. I good lucky a found one that was like the ST-70, original and unrestored. So I went to work and did all the usual stuff that most people do, I reworked the power supply and added a fuse and a turn on relay for the two switched outlets in the back of the unit. I did not recap the pre amp yet but I did replace the two capacitors coming off the tone controls.
Once I was satisfied that I hadn’t screwed anything up in either unit, I then decided it was time to give them a go so then I can at long last hear what all the fuss is about tube audio.
I hooked everything up and with my fingers crossed I slid the power switch on the PAS to the power position and it all came to life. I must admit I was a little nervous and excited at the same time. Anyways. I wasn’t sure I was impressed initially as I was using a pair heathkit as37 speakers that I have on my bench that sound ok but nothing at all special. I wasn’t ready to hook this thing up to my AR3a’s yet. So as I listened to some classic eagles music, I sat down and gave it a long listen while watching the bias and line voltage, trying to maintain a consistent 117 volts using a variac.
As I continued to listen. It was clear to me that it does indeed sound different than solid state. Once I adjusted the tone controls. I left it alone and listened to the entire disc 1 of the Eagles best of and I now must say I really do enjoy listening to this thing. Even with these unremarkable speakers I was really enjoying myself. Maybe I’m just stroking myself but, I do know the sound is different.
I will listen to it for a couple more days like this and then give it a whirl with the AR’s. I’m expecting a really big difference than with my puny Bench speakers.
I’ll be back. But in the meantime, here are a few pictures of mostly what I did to the PAS3x.
This is what it looked like when it arrived.
Attachments
Lavane
Lunatic Member
Congrats!, very nice.
I had restored an old console amp, then built a 300B SET amp.
But after building a VTA ST-70 I was totally sold on tubes and wound up selling off most of my SS gear along with setting a couple of my kids up with nice SS systems. I just don't see ever going back.
I had restored an old console amp, then built a 300B SET amp.
But after building a VTA ST-70 I was totally sold on tubes and wound up selling off most of my SS gear along with setting a couple of my kids up with nice SS systems. I just don't see ever going back.
topgun
Active Member
I plan on doing just that.
albusark
Dynaco Fan
Hey there, you 100% need to replace the coupling caps at the minimum. I personally replace all resistors and caps, it takes an afternoon per unit for me to do properly and test. A fully restored PAS preamp is absolutely stunning to listen to, the great majority of non-fans you'll take a look at the amp they based their opinion on and its in deplorable state with 60+ year old worn out components, usually it's just a can cap and the filament supply replaced.
albusark
Dynaco Fan
If you're feeling a very low level hum, quiet to the ear but tangible to your fingers when touching your speaker cone, chances are you need to replace the choke in your ST-70, or inspect the power section.
topgun
Active Member
I do realize that there ma be some more work to be done. I will also look into the situation with the choke.
And as far as the PAS goes. I am going to replace all the capacitors and resistors with metal film types. I did check all of the resistors in both units and did not find any that were out of tolerance. But like I said, I was still going to replace them anyway. I was just looking to hear them in as much as original condition as possible.
And as far as the PAS goes. I am going to replace all the capacitors and resistors with metal film types. I did check all of the resistors in both units and did not find any that were out of tolerance. But like I said, I was still going to replace them anyway. I was just looking to hear them in as much as original condition as possible.
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topgun
Active Member
That is the impression that I get when researching the PAS pre amp. It makes total sense that if something of that age which hasn’t been serviced and or upgraded is more than likely not work or sound as it should. Like I’ve posted, my pre amp has had the modifications that are geared toward reliability and not sound quality. So obviously it still needs some work. And still I found it to be a very good sounding piece. Looking forward to continuing the work on both it and the amplifier. There must have been a big reason that they sold so many for so long.
topgun
Active Member
I do understand what you mean. I’ve got a room full of solid state gear and this thing to me seems to sound very different but in a good way.
Lavane
Lunatic Member
I kept a few pieces of SS gear. The funny thing is what I kept isn't any of the TOTL SS gear I had collected. I kept what I listened to most.
Ooooh pretty! NIce work!