Just Pulled the trigger on Bob Latino's VTA-120 tube power amp.

[Drummerboy2]

So I will finally be getting a Tube power amp. I called Bob and we spoke for a while on the phone and he answered all of my question I had. Very nice man! I have been wanting a nice tube power amp for a while but the prices are just too much for the amount of power you are getting. So I have been looking/reading all I could find on the Bob Latino VTA-120 tube power amp and finally purchased one.

I was going to go for the M125 but I will be building a pair of 2 way GPA drivers with a Zilch Z19 xover so the VTA-120 should be enough for my setup.

I will be using the GZ34 (JJ, Mullard, and Ruby) rectifiers with this amp. I got the Cap upgrade also!

Any thing else to add?

Thanks

 

[asilker]

Very exciting. Looking forward to seeing some photos! I love my vta st70

 

[sKiZo]

Good choice! I love mine!

Exceptional sound quality and very nice components, playing well above it's price point. Some thought went into providing a robust and basically bulletproof amplifier. Yes, it's based on the old Dynacos (which were quite nice) but some serious upgrades to the iron and driver board really make them sing. I push mine to ear bleeding SPLs regularly (what can I say - prog rock - curse you Porcupine Tree!) and nary an issue. I also do dynamic expansion and bass synthesis, both of which will make a lot of amps go crying home for their mommies, and nary a wimper with the ST120. If it does clip, it's a very soft clip, and hardly noticeable.

I highly recommend the KT120 for power tubes. You'll never see the full rated output of the tubes, but that's a good thing in that they should last, like, forever as you're not driving them that hard in an amp that's built for KT88's. Good strong bottom end and crisp, clear middle. Also a real deal. The iron is more than enough to handle the extra demand gracefully, and you should see a good solid 70wpc.

Only real complaint I've ever heard is they can eat the Chinese 5AR4 rectifiers. If you can score a NOS Mullard, that's a good thing. I use a GZ37 here, and as I mentioned, I work it hard with excellent results.

DO follow the instructions! Bob includes a very well laid out assembly guide. I checked mine off at each step and highlighted anything I had to go back to (stuff like "don't solder yet" as there's more stuff to do here later). Once done, I went back and checked off each checkmark to verify I was good. One last close eye inspection, then follow the suggested plan for first fire. DO invest in a good solder station (big fan of the Weller WES51 analog here) as the cheap pencils ain't gonna cut it for point to point wiring. Do the assembly somewhere you can take your time ... no pushing to giterdone because it's time for dinner and the table's gotta be cleared ... <G>

Oh. Biggest common problem other than cold solder joints (practice!) is not trimming your leads properly. The VTA board especially is quite tight to the metal chassis, and leaving a cap lead long can cause shorts ... never a good thing.

 

[rebellovw]

Great choice - it will be a very fun build.

 

[GD70]

Oooo, can't wait to see pics of the build! Exciting!

 

[thorpej]

Only real complaint I've ever heard is they can eat the Chinese 5AR4 rectifiers. If you can score a NOS Mullard, that's a good thing. I use a GZ37 here, and as I mentioned, I work it hard with excellent results.

Have to be honest... it boggles my mind that people bother with vacuum rectifiers in new builds. I understand keeping the original rectification technology for restorations, or if you're looking for power supply sag in a guitar amp, but for new hi-fi builds (even clones) it seems like you want the power supply to have as little impedance as possible.

That said, I'm looking forward to seeing glamor shots of the completed build. Hooray for New Amp Day!

 

[Drummerboy2]

Very exciting. Looking forward to seeing some photos! I love my vta st70

I will try to post some pics as I go along and when finished. I'm very excited to hear it pared with my BAT VK-30 preamp once done. I was surprised to hear when Bob told me he has a BAT VK-30 SE connected to his VTA amps in his main system. He said they sound great together and uses them to audition his gear. can't wait!

 

[Drummerboy2]

Good choice! I love mine!

Exceptional sound quality and very nice components, playing well above it's price point. Some thought went into providing a robust and basically bulletproof amplifier. Yes, it's based on the old Dynacos (which were quite nice) but some serious upgrades to the iron and driver board really make them sing. I push mine to ear bleeding SPLs regularly (what can I say - prog rock - curse you Porcupine Tree!) and nary an issue. I also do dynamic expansion and bass synthesis, both of which will make a lot of amps go crying home for their mommies, and nary a wimper with the ST120. If it does clip, it's a very soft clip, and hardly noticeable.

I highly recommend the KT120 for power tubes. You'll never see the full rated output of the tubes, but that's a good thing in that they should last, like, forever as you're not driving them that hard in an amp that's built for KT88's. Good strong bottom end and crisp, clear middle. Also a real deal. The iron is more than enough to handle the extra demand gracefully, and you should see a good solid 70wpc.

Only real complaint I've ever heard is they can eat the Chinese 5AR4 rectifiers. If you can score a NOS Mullard, that's a good thing. I use a GZ37 here, and as I mentioned, I work it hard with excellent results.

DO follow the instructions! Bob includes a very well laid out assembly guide. I checked mine off at each step and highlighted anything I had to go back to (stuff like "don't solder yet" as there's more stuff to do here later). Once done, I went back and checked off each checkmark to verify I was good. One last close eye inspection, then follow the suggested plan for first fire. DO invest in a good solder station (big fan of the Weller WES51 analog here) as the cheap pencils ain't gonna cut it for point to point wiring. Do the assembly somewhere you can take your time ... no pushing to giterdone because it's time for dinner and the table's gotta be cleared ... <G>

Oh. Biggest common problem other than cold solder joints (practice!) is not trimming your leads properly. The VTA board especially is quite tight to the metal chassis, and leaving a cap lead long can cause shorts ... never a good thing.

I saw on YouTube that Audio Research uses the KT120's and how they let them burn in for a few days to let them settle in and bring out their sonics better. From what I'm hearing these are very good sounding tubes from Tung-Sol.

I will be pre-cleaning and tinning all the leads of resistors, caps, sockets, and wires to help insure against cold solder or open solder joints. I believe in taking the extra time to do this right so I won't have to worry about this stuff later if some is wrong or later on down the road years from now. I do have good solder irons and desoldering station. Yes, I do need to set a dedicated site to do this away from any disturbance.

 

[gadget73]

Solid state rectification would be a very good idea on this. The ST70 over-worked the rectifier, attempting to nearly double the power output without upgrading the rectifier is simply a bad idea.

 

[Drummerboy2]

Solid state rectification would be a very good idea on this. The ST70 over-worked the rectifier, attempting to nearly double the power output without upgrading the rectifier is simply a bad idea.

If you are referring to using the Weber Solid State rectifier, I have read some horror stories about them too. I have some different rectifiers on hand and will looking into the best one for my amp but I'm just hearing thing on all types of rectifiers. Thank You for the heads up though, I really appreciate it!

 

[sKiZo]

If you want a simple plug and play solid state solution, apparently the go to nowadays is the Weber WS1.

http://www.tedweber.com/ws1

The "horror stories" you heard are rare meltdowns using the WS34 or less so, the WS68. The WS68 is what I've got for backup. Just be aware, the WS1 does NOT provide slow start up like the other two. I think Weber had a lot to do with recent concerns when they added a "not for audio equipment" disclaimer to all their stuff except the WS1. Thing is, that's ALWAYS been their recommendation - the "new" disclaimers are just something they finally posted up along with a complete website redesign. Also, if the WS34 or WS68 do fail, they usually just stop working with no other damage. Both the WS34 and WS68 go for the same price, and the WS68 can handle twice the current, so that's pretty much a no brainer there. My recommendation if you DO go with a WS1 is to also add the TDR board to give you the slow start to limit the inrush on power up.

There's also solid state rectification options you can build right in to replace the bottle rectifier. Those are well documented elsewhere.

That said, I do so prefer the glowing warmth of a tube ... and yes, I CAN hear the difference. The Mullard GZ37 stands tall amongst the rest of the big trees ... ;-}

Solid state rectification would be a very good idea on this. The ST70 over-worked the rectifier, attempting to nearly double the power output without upgrading the rectifier is simply a bad idea.

ST70 spec'd 450 B+ ... the ST120 around 500, so not much difference there. Yes, at full drive, the additional watts will push the amp harder, but that's mostly an iron issue, and the transformers are a LOT stronger than the old Dynaco versions.. Lots of ST120's out there that have had no rectifier issues with "normal" use. Biggest problem is that the new production rectifiers aren't as robust as the old school favorites. There's a reason the Mullards command the prices they do, but they tend to last forever, so a bargain in the long run.

 

[Drummerboy2]

If you want a simple plug and play solid state solution, apparently the go to nowadays is the Weber WS1.

http://www.tedweber.com/ws1

The "horror stories" you heard are rare meltdowns using the WS34 or less so, the WS68. The WS68 is what I've got for backup. Just be aware, the WS1 does NOT provide slow start up like the other two. I think Weber had a lot to do with recent concerns when they added a "not for audio equipment" disclaimer to all their stuff except the WS1. Thing is, that's ALWAYS been their recommendation - the "new" disclaimers are just something they finally posted up along with a complete website redesign. Also, if the WS34 or WS68 do fail, they usually just stop working with no other damage. Both the WS34 and WS68 go for the same price, and the WS68 can handle twice the current, so that's pretty much a no brainer there. My recommendation if you DO go with a WS1 is to also add the TDR board to give you the slow start to limit the inrush on power up.

There's also solid state rectification options you can build right in to replace the bottle rectifier. Those are well documented elsewhere.

That said, I do so prefer the glowing warmth of a tube ... and yes, I CAN hear the difference. The Mullard GZ37 stands tall amongst the rest of the big trees ... ;-}

hi skizo, I just placed an order for the WS1 and WS68 just incase. I will order the delay circuit from Bob later. I'm sure I can put a NTC like the CL90 or some other size in to slow down the burst of the Weber WS1 on turn on. I would have to see the schematics to see what else to do. Don't know how this would affect the sound. But it would be nice to save/extend tube life.

 

[sKiZo]

I have a CL90 on mine. Doesn't seem to hurt anything. The B+ does come in a bit lower as a thermistor never opens completely, but it's still in range. I lose more B+ using a bucker to drop the line voltage to about 117vac, but once again, still within the recommended range.

Just make sure you provide plenty of clearance around the CL90 as they do get HOT. I expect that might be a challenge in the stock Dynaco chassis as there's not much ventilation or open space to work with.

PS ... I'm sure some will notice the CL90 isn't rated high enough to handle the ST120's current requirements. Use a CL80 they'll say. Pshaw ... I've used CL90's in equipment drawing twice, even three times the rated current with no problems. Main reason I use it is the CL90 has much better heat dissipation than the higher rated CL80.

 

[Dandy]

FWIW, when I put in a bigger power transformer in my ST70 and needed a biggish voltage drop, I went for a 5R4. It has woken up my amp a lot. So, down the line it might be worth trying other tube or solid state rectification. I also prefer the sound of tube rectification.

 

[AlTinkster92]

This looks like a thread I need to watch and learn from, Al

 

[Drummerboy2]

I have a CL90 on mine. Doesn't seem to hurt anything. The B+ does come in a bit lower as a thermistor never opens completely, but it's still in range. I lose more B+ using a bucker to drop the line voltage to about 117vac, but once again, still within the recommended range.

Just make sure you provide plenty of clearance around the CL90 as they do get HOT. I expect that might be a challenge in the stock Dynaco chassis as there's not much ventilation or open space to work with.

PS ... I'm sure some will notice the CL90 isn't rated high enough to handle the ST120's current requirements. Use a CL80 they'll say. Pshaw ... I've used CL90's in equipment drawing twice, even three times the rated current with no problems. Main reason I use it is the CL90 has much better heat dissipation than the higher rated CL80.

sKiZo, The CL90 @100% has a resistance of 1.18 ohms so that's not too bad and with the SS rectification should be negligible. I just like at the dead start it's @ 120 ohms compared to the CL80 47ohms but @ 100% has .49ohms which is better. Just depends on how slow you want the inrush.

Would the CL90 or 80 go in between the power switch for the B+ voltage and power transformer or on the line after the rectifier like some others do? I was going to put mine between the power switch and power transformer for the B+ like in my SS amp.

 

[Drummerboy2]

I have a CL90 on mine. Doesn't seem to hurt anything. The B+ does come in a bit lower as a thermistor never opens completely, but it's still in range. I lose more B+ using a bucker to drop the line voltage to about 117vac, but once again, still within the recommended range.

Just make sure you provide plenty of clearance around the CL90 as they do get HOT. I expect that might be a challenge in the stock Dynaco chassis as there's not much ventilation or open space to work with.

PS ... I'm sure some will notice the CL90 isn't rated high enough to handle the ST120's current requirements. Use a CL80 they'll say. Pshaw ... I've used CL90's in equipment drawing twice, even three times the rated current with no problems. Main reason I use it is the CL90 has much better heat dissipation than the higher rated CL80.

Since others are using 1N4007's in DIY rectifiers for tubes, I wonder how a Schottky High Voltage High current rectifier would work and sound. If it hasn't been tried yet might be something to try making for my amp. Or just us a Schottky module.

 

[sKiZo]

Would the CL90 or 80 go in between the power switch for the B+ voltage and power transformer or on the line after the rectifier like some others do? I was going to put mine between the power switch and power transformer for the B+ like in my SS amp.

I just put mine on the hot AC lead in ...

No load condition when the power's off, so no problem. Since taking the pic, I did move that blue wire away ... did I mention those thermistors get HOT? <G>

No experience with the Schottky ...

Oh. One BIG improvement you can make to your system. Tube amps need time to discharge properly on shut down and do NOT like quick power cycling, like the BLIP BLIP crap you get in a lightning storm. Big fan of this NON-LATCHING adapter. It can handle plenty of amps, and must be manually reset whenever it's tripped. I use one for both my ST120 and an Eico HF12a I use to drive a center channel.

TRC 90033 Shockshield White Portable GFCI Plug with Surge Protection

(Ignore the GFCI feature ... it's the "non-latching" bit that can save your bacon.)

 

[rebellovw]

I had a weber burn up in mine and take out a power tube. I have a new set - but they are sitting in a drawer - only for backup.

 

[thorpej]

ST70 spec'd 450 B+ ... the ST120 around 500, so not much difference there. Yes, at full drive, the additional watts will push the amp harder, but that's mostly an iron issue, and the transformers are a LOT stronger than the old Dynaco versions.. Lots of ST120's out there that have had no rectifier issues with "normal" use. Biggest problem is that the new production rectifiers aren't as robust as the old school favorites. There's a reason the Mullards command the prices they do, but they tend to last forever, so a bargain in the long run.

It's not so much the voltage (vacuum rectifiers are usually pretty rated pretty high -- 5AR4 is 1500V PIV), but rather the current (5AR4 is rated at 250mA DC current as Design Center max). Sure, you can exceed that a bit, probably, and be OK, possibly. But geez, 250mA is nothing. I just built a 30W/ch amp whose finals idle at a combined 212mA (and then there's 18mA of constant current for both channels' phase inverters and another 1.5mA for the first stage). That right there is already close to taxing a 5AR4. A GZ37 isn't much better, rating-wise, unless you're using a choke input filter. It's easy to see why the ST-70 was hard on rectifiers.

My go-to rectifier is the Vishay GBPC3510-E4/51 if I need a full-wave bridge... $5 at Mouser, easy mounting against the chassis, and it's good for 35A of continuous forward current (i.e. total overkill) with a 1.1V drop and you can safely use it with secondary windings up to ~600VAC [edit: typo]. If you're really worried about it burning out, put a fuse on your PT secondary. If you have a center-tapped PT you're going to need to spring for diodes that can handle 1400V or 1500V PIV if your PT is bigger than, say, 300-0-300 (600VCT). But even then you're talking $1 a piece for fairly beefy ones (like the Vishay BY228GP-E3/54, which is good for 2.5A continuous forward current and 50A surge current -- WAY more than enough for a tube amp). In this case, you need a fuse on each secondary lead.