Good point; also, 100 mfd for the first filter node is way way too much for a 5AR4/GZ34. 40 to 50 mfd tops, and adding diodes inline with the rectifier tube plates would also be a good idea. I left some other related thoughts in a comment above.
100 mfd total for the first filter node is roughly double the recommended maximum capacitance for a GZ34/5AR4, especially if you're using a modern Chinese or Russian rectifier tube, which are far less rugged than a vintage Mullard. I'd shoot for a 40 mfd first-filter node, and add series diodes (1N5408 would be a good chiece, perhaps two in series per plate) between the B+ secondary and the plates of the rectifier tube. Also, as somebody else mentioned below, that stock standby switch arrangement kills rectifier tubes, and beats up the switch contacts as well (they'd be prone to arcing). 600 DC volt rated switches are hard to find; I'd put the switch in line with the AC B+ *before* the rectifier (AC is less likely to arc and spark), though there are other methods/locations for the standby switch. Anyway, if the input to the rectifier tube has series diodes inline, and you keep the first filter node to 40 mfd, you could probably use less expensive NOS 5U4 rectifiers instead of expensive, and often rattle-prone, 5AR4/GZ34; a 5U4 would lower the blazing voltages a bit, therefore gentler on caps and tubes, and adding a little sag and compression, which might or might not be acceptable to certain players. I seriously question whether that small choke can handle *ALL* the current for the entire circuit (Fender used a choke for the output screens and the preamp supply), but if youre sure the choke can handle several hundred milliamps of current to the KT88 plates/screens, then perhaps you should design the power supply as a *choke input filter* and put the first filter-cap *AFTER* the choke. Choke-input filters are much gentler on the rectifier tube.....
The doubling of the caps in series the way I did reduces the mfd. However, it didn't balance well and was still to much. I was getting like 70mfd, and even tho the rectos were handling it, it was hard on them and I had to jump start the amp with diodes. This will make more sense in following episodes. The PSU gets adjusted, and the Standby gets changed. I've thought of putting trying a 5U4 but I'm afraid to blow one, even tho I think it'll be fine. I currently run a soviet surplus 5U4C, which is suppose to be too small, hah. I didn't consider the choke, it's the stock choke, I'd like to think they used the right choke for the circuit. I don't even know the rating of the stock choke. Now that you mention that, I wonder if the choke, is choking current flow, cause this amp won't put out more than 50w, typically 35-40watts cranked. Not sure if my mods have reduced it's output, but then, the preamp design, I believe, doesn't have the most drive to begin with.
@@DATT , a 5U4 can likely handle the voltage, especially with a 30 to 40 mfd max capacitance load and diodes feeding the 5U4 plates (so that the only thing the 5U4 does is give you a slightly slower be plus rise time and lowers the overall voltage to the circuit a little bit). The 5U4 does draw 50% more filament current than a 5AR4 but those big Transformers should easily be able to handle it. For reliability I'd take a vintage 5U4 over a Chinese or Russian 5AR4, and the vintage rectifier shouldn't cost very much. Another rectifier tube possibility would be the 5R4, especially if you use one of the gigantic, flat-top mil-spec "potato masher" 5R4's made by Chatham Electronics and others. If you've never seen one of those, Google it; theyre impressive looking,, and were made to work in high-flying bomber planes under low pressure, near-vacuum atmospheric conditions!
@@goodun2974 Yeah I don't do the series diode thing, I guess you still get tube sag, but, it's like what's the point if the circuit is working right. I am newer to tube recto circuits tho, maybe my opinion will change. I just built 2 amps with tubes rectos, so far so good. I actually torture tested the main 6v fil supply on this tran, to see if it could burn GU-29 tubes and it didn't even break a sweat. I'm surprised how cheap old 5U4GB's are on ebay, bought a couple recently. I almost dont' get it, cause old 5AR4's they are asking a lot. I'm familiar with the 5R4, never owned one tho, one day I'm sure. I recall their ratings had the most drop of all the common tubes.
@@DATT , 5AR4's have an independentky-heated cathode, while 5U4, 5R4 and 5Y3 use the filament as the cathode. The independent cathode of the 5AR4 allows for closer spacing of plates to cathode, providing less voltage drop without arcing, compared to the filament-type rectifiers; BUT, that was with high-quality American and European tubes. The 5AR4 was more expensive to make and was a late addition which was developed near the end of the tube era; most US manufacturers never tooled up to make them and merely imported and rebranded Mullard or Amperex 5AR4's, so there aren't many of them around nowadays, and they command a premium price. Anyway, modern tubes aren't built to the same standards, and you can't just pop down to the corner tv/radio shop or even the drugstore for high-quality replacement tubes. The added diodes make life much easier for the rectifier, providing freedom from arcing, and I strongly recommend using them, especially because modern wall voltages are high and full of noise and voltage spikes.
@@goodun2974 Hmm, I was aware of the heater distances, but not the point of it being to lower the votlage drop. That make sense. The Soviet 5U4C I was using has the cathode like the 5AR4, but a lower mA spec like a 5Y3, so far it's been fine in the amp the way I run it. Sadly, I did . . . blow a 5U4C in my Vibrolux Reverb the other day. Seems it can handle running a 50w amp flat out. I just put a 5U4GB in this amp to try. An old "Raytheon". Seems fine, and the voltage dropped to 533v without biasing. It was 565 with the 5U4C and 575 with a 5AR4.
Oh totally agreed, "valuable" BAD/TOTALLY USELESS PARTS! the organe capacitor is definitely worth at least $12,750, bad, on eBay. Double that if it tests anything less than 50% out of spec.. and don't forget to buy the special audiophile fuses while you're in there 😆(my how eBay has become such a dumpster fire). I stopped messing with vintage gear when it went full-on "$15,000 for a 300,000 mile 2008 base model Camry" levels of stupid lol
Yeah, I didn't even think about that at the time. I slapped it down onto the original footprint, where I might assume that certain fundamentals like that have already been figured out my the original makers.
A high-power bass head is absolutely the worst type of amplifier for having replaced components floating in mid-air, because constant vibration from the speaker cabinet will eventually fatigue and break the leads.
There's extra holes in these chassis, why didn't you just leave the can in there and then put some terminal strips and use some axials like a Fender with balance resistors instead of putting another big hole in it. Also Triode has the transformers for these amps, they are an ultra linear design from Dynaco.
Yes! I've restored many 60 watt Sunn amps this way. Lots of great axial caps available from F & T. The earliest Sunn amps were literally Dynaco Mark III power amps with a tweaked knock-off a a Dynaco preamp. Ultra linear OT in the power amp for lots of clean bass. Rear-loaded bass reflex cabinet with a pair off JBL D-140's. Beat both Fender and Marshall for bass in the late 60's. Yeah, Triode carries the correct OT.
That some good info, I don't know much about Sunn, I might have to study some Dynaco Schems. And I made the hole cause I wanted to use up some caps I already had and there was room to do it nice. It was kind of a Judgment call at the time, especially since this head would never see an original output transformer again, it made it already modded and unoriginal so I just went with the flow.
Long time no view. Love your madness, bud!
Hell Yeah !
That standby switch is wired in a way that destroys rectifier tubes. Check valve wizard on how to convert it to a better one :) Nice video, thanks
Good point; also, 100 mfd for the first filter node is way way too much for a 5AR4/GZ34. 40 to 50 mfd tops, and adding diodes inline with the rectifier tube plates would also be a good idea. I left some other related thoughts in a comment above.
Absolutely, I fix it in future Episodes.
And yeah, 100 is too much, the idea is it's split down to 50 in this config, but it was still too much, and gets changed later.
Just what the doctor ordered
Quite Possibly.
100 mfd total for the first filter node is roughly double the recommended maximum capacitance for a GZ34/5AR4, especially if you're using a modern Chinese or Russian rectifier tube, which are far less rugged than a vintage Mullard. I'd shoot for a 40 mfd first-filter node, and add series diodes (1N5408 would be a good chiece, perhaps two in series per plate) between the B+ secondary and the plates of the rectifier tube. Also, as somebody else mentioned below, that stock standby switch arrangement kills rectifier tubes, and beats up the switch contacts as well (they'd be prone to arcing). 600 DC volt rated switches are hard to find; I'd put the switch in line with the AC B+ *before* the rectifier (AC is less likely to arc and spark), though there are other methods/locations for the standby switch. Anyway, if the input to the rectifier tube has series diodes inline, and you keep the first filter node to 40 mfd, you could probably use less expensive NOS 5U4 rectifiers instead of expensive, and often rattle-prone, 5AR4/GZ34; a 5U4 would lower the blazing voltages a bit, therefore gentler on caps and tubes, and adding a little sag and compression, which might or might not be acceptable to certain players.
I seriously question whether that small choke can handle *ALL* the current for the entire circuit (Fender used a choke for the output screens and the preamp supply), but if youre sure the choke can handle several hundred milliamps of current to the KT88 plates/screens, then perhaps you should design the power supply as a *choke input filter* and put the first filter-cap *AFTER* the choke. Choke-input filters are much gentler on the rectifier tube.....
The doubling of the caps in series the way I did reduces the mfd. However, it didn't balance well and was still to much. I was getting like 70mfd, and even tho the rectos were handling it, it was hard on them and I had to jump start the amp with diodes. This will make more sense in following episodes.
The PSU gets adjusted, and the Standby gets changed.
I've thought of putting trying a 5U4 but I'm afraid to blow one, even tho I think it'll be fine.
I currently run a soviet surplus 5U4C, which is suppose to be too small, hah.
I didn't consider the choke, it's the stock choke, I'd like to think they used the right choke for the circuit. I don't even know the rating of the stock choke. Now that you mention that, I wonder if the choke, is choking current flow, cause this amp won't put out more than 50w, typically 35-40watts cranked.
Not sure if my mods have reduced it's output, but then, the preamp design, I believe, doesn't have the most drive to begin with.
@@DATT , a 5U4 can likely handle the voltage, especially with a 30 to 40 mfd max capacitance load and diodes feeding the 5U4 plates (so that the only thing the 5U4 does is give you a slightly slower be plus rise time and lowers the overall voltage to the circuit a little bit). The 5U4 does draw 50% more filament current than a 5AR4 but those big Transformers should easily be able to handle it. For reliability I'd take a vintage 5U4 over a Chinese or Russian 5AR4, and the vintage rectifier shouldn't cost very much. Another rectifier tube possibility would be the 5R4, especially if you use one of the gigantic, flat-top mil-spec "potato masher" 5R4's made by Chatham Electronics and others. If you've never seen one of those, Google it; theyre impressive looking,, and were made to work in high-flying bomber planes under low pressure, near-vacuum atmospheric conditions!
@@goodun2974 Yeah I don't do the series diode thing, I guess you still get tube sag, but, it's like what's the point if the circuit is working right. I am newer to tube recto circuits tho, maybe my opinion will change. I just built 2 amps with tubes rectos, so far so good.
I actually torture tested the main 6v fil supply on this tran, to see if it could burn GU-29 tubes and it didn't even break a sweat.
I'm surprised how cheap old 5U4GB's are on ebay, bought a couple recently. I almost dont' get it, cause old 5AR4's they are asking a lot. I'm familiar with the 5R4, never owned one tho, one day I'm sure. I recall their ratings had the most drop of all the common tubes.
@@DATT , 5AR4's have an independentky-heated cathode, while 5U4, 5R4 and 5Y3 use the filament as the cathode. The independent cathode of the 5AR4 allows for closer spacing of plates to cathode, providing less voltage drop without arcing, compared to the filament-type rectifiers; BUT, that was with high-quality American and European tubes. The 5AR4 was more expensive to make and was a late addition which was developed near the end of the tube era; most US manufacturers never tooled up to make them and merely imported and rebranded Mullard or Amperex 5AR4's, so there aren't many of them around nowadays, and they command a premium price. Anyway, modern tubes aren't built to the same standards, and you can't just pop down to the corner tv/radio shop or even the drugstore for high-quality replacement tubes. The added diodes make life much easier for the rectifier, providing freedom from arcing, and I strongly recommend using them, especially because modern wall voltages are high and full of noise and voltage spikes.
@@goodun2974 Hmm, I was aware of the heater distances, but not the point of it being to lower the votlage drop. That make sense.
The Soviet 5U4C I was using has the cathode like the 5AR4, but a lower mA spec like a 5Y3, so far it's been fine in the amp the way I run it. Sadly, I did . . . blow a 5U4C in my Vibrolux Reverb the other day. Seems it can handle running a 50w amp flat out.
I just put a 5U4GB in this amp to try. An old "Raytheon". Seems fine, and the voltage dropped to 533v without biasing. It was 565 with the 5U4C and 575 with a 5AR4.
Oh totally agreed, "valuable" BAD/TOTALLY USELESS PARTS! the organe capacitor is definitely worth at least $12,750, bad, on eBay. Double that if it tests anything less than 50% out of spec.. and don't forget to buy the special audiophile fuses while you're in there 😆(my how eBay has become such a dumpster fire). I stopped messing with vintage gear when it went full-on "$15,000 for a 300,000 mile 2008 base model Camry" levels of stupid lol
Yeah, I have a lot of strong opinions on "vintage gear" and it's value.
I wonder if it would be worth rotating the new ot 90° ? Or are they far enough apart?
Yeah, I didn't even think about that at the time. I slapped it down onto the original footprint, where I might assume that certain fundamentals like that have already been figured out my the original makers.
A high-power bass head is absolutely the worst type of amplifier for having replaced components floating in mid-air, because constant vibration from the speaker cabinet will eventually fatigue and break the leads.
Oh hell yeah, I try to secure as much as I can.
There's extra holes in these chassis, why didn't you just leave the can in there and then put some terminal strips and use some axials like a Fender with balance resistors instead of putting another big hole in it. Also Triode has the transformers for these amps, they are an ultra linear design from Dynaco.
Yes! I've restored many 60 watt Sunn amps this way. Lots of great axial caps available from F & T. The earliest Sunn amps were literally Dynaco Mark III power amps with a tweaked knock-off a a Dynaco preamp. Ultra linear OT in the power amp for lots of clean bass. Rear-loaded bass reflex cabinet with a pair off JBL D-140's. Beat both Fender and Marshall for bass in the late 60's. Yeah, Triode carries the correct OT.
That some good info, I don't know much about Sunn, I might have to study some Dynaco Schems.
And I made the hole cause I wanted to use up some caps I already had and there was room to do it nice.
It was kind of a Judgment call at the time, especially since this head would never see an original output transformer again, it made it already modded and unoriginal so I just went with the flow.
Hey were are you located ? I am in the GTA area and was looking to have my JCM tunned up. Do you have a contact number were I can reach out to you ?
No, I'm in Ontario, but rather far from the GTA. The cost to get the amp to me alone would cost many 100's.