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    Building, troubleshooting and testing of these amplifiers should only be
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Upgrading my Audio Research VT 130 SE Tube amp

Serratoga

Member
2006-10-23 10:38 am
Hi Everyone,
I was hoping to get some advice on upgrading my VT 130SE. It has 4x 6550 , 1x 12BH7 driver
tube and 2x 6922 input tubes per channel. It also has 4x large mallory 800 Uf 450V Capacitors
screw type. I was told by Audio Research to upgrade my MIT Multicap coupler caps it has 2 per channel, to the infinicap signature ($30.00 each .68 Uf) or to the Infinicap M2A ( $50.00 each .68 Uf), WOW these are more expensive than the Mundorf Silver Gold and I am not so sure they are better than the Mondorf ?? it also has a fixed power cord in which is the original.
Any advice is appreciated.

Thanks

:)
 

prakit

Member
Paid Member
2005-01-18 6:12 am
Bangkok, Thailand
Hi,
I also have this amp. I've upgraded those 4 coupling caps to InfiniCap. Not sure if they are the signature serie since I did this 3-4 yrs ago. I could discern some improvement on clarity and extension but it also sounds less fluid in the mid. I'd try film and foil type if I were you. They sound much smoother. I have tried the older Infini cap in other applications and had the same conclusion on it's character.

I have done quite a few modifications to the amp. I suggest you replace the film cap at the regulator output with some film/foil cap. I used Hovland. The improvement was much greater than replacing the coupling caps for me. The amp sounded fuller and more dynamic.

The biggest improvement I achieved was from implementing constant current sources to those input and driver stages. The dynamic and bass slam and extension is among the best I've heard from a tube amp. You can check out the schematic of the VT100 on this.
 

Serratoga

Member
2006-10-23 10:38 am
Hi Prakit,
Thanks for the information. You know, I was debating about the the film and foil. Solen makes
some real nice "Film and Foil" caps. I used them in a crossover for a pair of Linn Keilidh , in the
tweeter section and they were beautiful, and I tried many, these were crystal clear at a fraction of the price , I have the main distributor near buy. Also there has been a lot of talk about using
The Mundorf "Silver in Oil" What are your thoughts?

Prakit,
I would like to replace the film cap at the regulator output but I am not sure which one it is ?
If you could point it out that would be great, I will definitly try it. if you could explain any other
mods in detail it would be a ton of help to me especially the section on adding
"constant current sources to those input and driver stages"

Thanks
Slate
 
Serratoga said:
I would like to replace the film cap at the regulator output but I am not sure which one it is ?


It seems to be C38 on my circuit. ARC don't seem to be too happy about loading this regulator with capacitance that's why they use a snubber. A different type of capacitor might need the snubber readjusted. Careful as it may start oscillating.

I'd also improve upon C8, C9, the caps filtering the fixed bias.

The VT100 circuitr seems altogether more attractive but obviously means a major surgery.
 

Serratoga

Member
2006-10-23 10:38 am
Hi analog,

"It seems to be C38 on my circuit. ARC don't seem to be too happy about loading this regulator with capacitance that's why they use a snubber. A different type of capacitor might need the snubber readjusted. Careful as it may start oscillating."

I checked the schematics on my ARC VT 130 SE and the c38 is a (Rel Cap PPMF 2.0 Uf @450v)
Analog are saying replacing this cap with a (Solen Film & Foil 2.0 Uf @ 400 v) may cause it to
oscillate ??

Thanks
Slate
 
If it is teflon film and tin foil then it is very likely better :)

Unless you discuss specific series it is difficult to make a general statement.

I would simply go for Multicap RTX which will largely preserve the sound character and bring in some improvement but then again i never go crazy with caps.

Not to mention that opamp (and associated capacitors) responsible for dc balance is probably a bigger liability then some coupling caps.
 

prakit

Member
Paid Member
2005-01-18 6:12 am
Bangkok, Thailand
Hi Slate,

I replaced C38 with a 0.47uF Hovland and later I added a 2.0uF Hovland across C38 and R71. The latter was soldered underneath the PCB. The improvement from doing this was very similar to when I added a choke to the raw supply of my diy preamp. The sound became fuller and palpable. Hard to explain.

About adding the constant current sources(CCS), besides the input stage it's quite easy to do. If you want to try this, I suggest you do it with the second stage and the driver stage. The R13A+B are two 5.11K resistors connected in series. One end of these are connected to cathode of V2, the other to ground. There's about 70V drop across these two resistors. I replaced the one next to the cathode with a CCS configured for about 7mA of current sinking for each triode.

For the driver stage, R23 and R24 were replaced with ccs configured for about 5.5mA of current sinking. I added a 15K in series with this ccs so that the voltage drop across the ccs inself is about 20V and no heatsink is needed.

I used LM334(low voltage current source) for the second stage but used IXCP 10M45S(rated 400V) for the driver stage. The improvement was shocking.

I didn't have experience with the oil imprognated caps but have a plan to try Mundorf Supreme on my newly acquired M100s.



:) :) :) :)
 

Serratoga

Member
2006-10-23 10:38 am
prakit said:
Hi Slate,

I replaced C38 with a 0.47uF Hovland and later I added a 2.0uF Hovland across C38 and R71. The latter was soldered underneath the PCB. The improvement from doing this was very similar to when I added a choke to the raw supply of my diy preamp. The sound became fuller and palpable. Hard to explain.

Prakit,
when you added the .47 Uf hovland on top and the 2.0 Uf on the under side was because of space constriction? Is it OK to increase the values from 2.0 Uf to 2.47 Uf ???
 

prakit

Member
Paid Member
2005-01-18 6:12 am
Bangkok, Thailand
Hi Slate,
It's because of space limitation that the 2.0uf had to go underneath. The cap was about 3" long. I didn't experience any oscillation problem from doing this.
 

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Hi Slate,

Read DaveT's thread about "Tripath Input Coupling Caps," it might help you decide to do with coupling caps. The most expensive wasn't the best. Read it through and you will find some surprises.

Of course this is a different amp but do your research! You just might get even better results, especially if you narrow down your choices based on your preferences.

Also since you have an AR Preamp you need to find the best match between the two at the handoff from the pre to the amp. You can tailor this for optimal results.

Also pay attention to what analog_sa was saying about the decoupling caps elsewhere in the circuit!

Again, burn in the caps before testing so you have a more accurate first impression.

Don't go crazy with the cost of caps so you can try a few and maybe a few combos too (bypassing)!

Regards//Keith
 

prakit

Member
Paid Member
2005-01-18 6:12 am
Bangkok, Thailand
Serratoga said:
I totally get it now, I see you have installed some Dynamicaps in the coupling section , how are they? And what values have you used?

They're 1.0uF. Slight improve on definition but also harder sounding. Very slight improvement, not a worthwhile upgrade.


Serratoga said:
I couldn't help noticing the work you did behind the 12BH7A,
is that a repair or an upgrade??

They are CCS in place of the original resistors.
 

Serratoga

Member
2006-10-23 10:38 am
I would like to take a moment and thank everyone in this thread, in helping make my decision.
I have decided to go with Mundorf Silver in oil for the coupling caps (.068 Uf @ 1200V) X4.
For the power supply I am going to go with the Multicap RTX (2.0 Uf @200V).
Prakit, thank you for advice and thank you for replying to me thread.
Keith what can I say, thanks for looking out for me, I am still waiting to put my crab together
but parts are slowly coming in, I have quite a bit of caps to burn, as I also ordered the infinicaps
ARC recommended , I will not be using them but the they are OEM parts for my amp, and I have learnt to keep OEM parts. In the mean time I have over 200 tubes to test on my tester,
and check which type are better suited for my equipment. ( Sound Tests ).

I will post my findings as soon as I am done...............
 
We might not see you for months!

Let me know if the crab gives you any problems. It can handle many caps if necessary, just grow more legs!

It's always good to have extra parts! Until you have no living space left! Then you can sell some!

Most of the time with coupling caps, the values are not a hard number. If you change the vaules (not crazy) it may affect the frequency response and roll off. There are formulas you can use to tune ideally to the output of your preamp. Then it is a matter of your preference of sound for which manufacturer and materials that please you most. Don't be afraid to experiment!

Most of all, enjoy yourself!

Regards//Keith

PS, Don't be afraid to try Wima MKP4s, Epcos B25834, Silver Micas and/or VR MKP1837s for bypassing, etc.
 

mallikh67

Member
2011-04-18 5:18 pm
Hi Everyone,
I was hoping to get some advice on upgrading my VT 130SE. It has 4x 6550 , 1x 12BH7 driver
tube and 2x 6922 input tubes per channel. It also has 4x large mallory 800 Uf 450V Capacitors
screw type. I was told by Audio Research to upgrade my MIT Multicap coupler caps it has 2 per channel, to the infinicap signature ($30.00 each .68 Uf) or to the Infinicap M2A ( $50.00 each .68 Uf), WOW these are more expensive than the Mundorf Silver Gold and I am not so sure they are better than the Mondorf ?? it also has a fixed power cord in which is the original.
Any advice is appreciated.

Thanks

:)
hi i am mallikh from india and i have a pair of arc vt150se and ls26 preamp.the q1,q2 fets used in

arc vt150se as there is no data on the components written