Help with Tubelab SE component selection

[OneLiterPeter]

Hi all!

First post and I'm already asking questions. I've built a few kits with good results, Bob Latino ST-120, Bottlehead Foreplay III and a Glassware Aikido All-In-One LSA. I've also done quite a bit of work on a YUSynth Modular synthesizer (long term project).

I've always wanted a Class-A single ended amp so I'm building a dedicated 300B Tubelab SE.

For this build I won't be pushing the envelope, I just want a nice clean solid build. With that said I have a few component questions. I already have the pcb populated with resistors and regulators. I've already purchased a Hammond 276X PT and two One Electron UBT-3 OPT's. Now I need to make decisions on what capacitors afford the best sound quality.

From Tubelab...

Capacitors C4 and C5 are however very important to the amplifier's sound and power output capabilities. Capacitor C4 is the input capacitor for the power supply. The value of this cap determines output voltage of the power supply. The larger the cap value, the higher the voltage. The value of this cap can be changed (within reason) to tweak the power supply voltage. The Amperex data sheet for the 5AR4 gives a maximum value of 60uF for this cap. This value can be exceeded at the risk of your 5AR4's lifetime. On low voltage applications you may get away with a larger value. The board can accommodate up to a 100uF 500Volt cap for C4. Some users may want to use their favorite brand of boutique capacitor here. There is a chart in the Applications page that will help you pick the value of C4. Some users will substitute an external choke for R4. This will require modifying the value of C4 to get the proper voltage, which is now dependent on the value of the choke and the value of C4.

I need some help selecting C4. My PT is a Hammond 276X with a 640V CT secondary.
What value should C4 be?
The component list has a 47uF 400V listed. Is this the correct cap for use with 300B tubes?
What favorite boutique caps are you using?
Is there a specific brand that is best?

My ST-120 also uses a 5AR4 regulator tube and I switched it out for a Weber Copper Cap with good results.
Has anyone used a Copper Cap in a TSE and if so is there any benefit?

There's also supposed to be a chart on the applications page but I can't seem to find it so any help would be appreciated.

C5 is the output capacitor for the power supply. Its value has a small effect on the output voltage. The quality of C5 has a dramatic effect on the amps sound quality. If you intend to upgrade any capacitor in the power supply, this is the one. My personal preference is to use a high quality electrolytic on the board, and connect an external (off board, mounted in the cabinet) paper in oil capacitor directly between the output transformer and the filament of the output tube. A film cap is also useful here. Details for these modifications are given on the upgrades page. I allocated the largest possible space on the board for C5. The value of this cap is not as important as the quality of the cap. Use a capacitor of at least 100 uF with a voltage rating appropriate for your transformer. Look for low ESR, inductance (ESL), and dissipation factor and make sure that it will fit in the board.

On the component list C5 is listed as a 150uF 450V electrolytic cap. The above excerpt also mentions the use of an offboard PIO cap as well as possibly using a film cap.

What brand/s of cap is a good choice for C5?
What is the value of the PIO cap should I choose to implement one?
Is it a good idea to go with a film cap, if so which one?

Sorry for asking such basic questions but whenever I click the link for the upgrades page it just shows a title and some menu choices along the left.

Finally I'm interested in which coupling caps people are using. George recommends using either the Orange drops, Auri Caps or Mallory film caps. I've also used PIO caps in my st-120 with good results.

Which of these caps would be best for my TSE 300B?
Can I use PIO's in place of these?

Thanks in advance for any and all help.

Pete

[rknize]

Originally Posted by OneLiterPeter

I need some help selecting C4. My PT is a Hammond 276X with a 640V CT secondary.
What value should C4 be?
The component list has a 47uF 400V listed. Is this the correct cap for use with 300B tubes?
What favorite boutique caps are you using?
Is there a specific brand that is best?

What George is talking about here is adjusting the value of C4 if needed to drop your B+ voltage. For 300Bs, 400V is probably your B+ goal. 47uF is about the right value for a 640CT secondary, but the Hammond 2xx series has a reputation for running hot. Some folk have dropped this value down to 10uF or less to get the B+ to drop a bit. You definitely don't want to use a larger value as it will strain the 5AR4 too much (47uF is already pushing it).

As far as brand, well opinions will obviously vary. Since there are stages of filtering that follow this cap, I don't personally see much point in using a boutique cap here. It needs to be at least 450V, obviously. 500V doesn't hurt. The spec'd part from CDE, Nichicon, Panasonic, etc will work fine IMO, but that is probably not the answer you are looking for.

My ST-120 also uses a 5AR4 regulator tube and I switched it out for a Weber Copper Cap with good results.
Has anyone used a Copper Cap in a TSE and if so is there any benefit?

The copper cap is nothing more than a couple of high voltage silicon diodes with some power resistors to simulate the tube drop of a vacuum tube. They are handy in that don't raise B+ the way straight silicon diodes do. The downside is that they are supposedly not very well constructed and they don't give you the delayed B+ rise that a real 5AR4 gives you.

In any case, the type you would need is the WZ34.

On the component list C5 is listed as a 150uF 450V electrolytic cap. The above excerpt also mentions the use of an offboard PIO cap as well as possibly using a film cap.

What brand/s of cap is a good choice for C5?
What is the value of the PIO cap should I choose to implement one?
Is it a good idea to go with a film cap, if so which one?

The quality of this cap is a little more important. A low ESR cap is helpful here. There is room on the PCB for a 220uF 500V cap, if you wish (this is what I have in mine). The part George specs is a good quality cap from Panasonic. Again, you can stick a boutique cap in here if you want. If you plan to put a film cap in parallel with it, then using a boutique cap doesn't make much sense. A lot of people use motor run caps here because they are a great value. Anything in the 60-100uF range is commonly used.

Of course you can just use one giant film cap for all of the caps on the board. Someone here built an SSE using all film caps. Obviously, they are huge and won't fit on the PCB. Just use something that at least meets George's specs (120uF@450V for C5).

Finally I'm interested in which coupling caps people are using. George recommends using either the Orange drops, Auri Caps or Mallory film caps. I've also used PIO caps in my st-120 with good results.

Which of these caps would be best for my TSE 300B?
Can I use PIO's in place of these?

Of course. Russian PIOs are a popular choice. You can use whatever you want as long as it meets the minimum spec. You can actually go with a lower capacitance if the amp will not be driving the low frequencies. Opinions here vary even more than the PSU caps.

Capacitor brands are one of those things where opinion will vary all over the place. Tubelab and a number of it's builders tend to be a bit more budget-minded and therefore a bit more down-to-earth about how much they are will to spend on a capacitor. That's not to say that a quality cap isn't important. Also, there are people that dropped some serious coin into their amps.

It's a lot like tube choices and the law of diminishing returns weighs heavily here. You spent some money on those UBT-3s and that was money well-spent. It's pretty easy to swap coupling caps and very easy to swap tubes later on.

All that said, I have used those Orange Drops, Russian PIOs, and Auricaps in mine. The latter is what is in there now and I like them the best...they have the most detail and transparency...something the TSE excels in on my system.

[OneLiterPeter]

Thanks for sharing your expertise Russ, It's appreciated.

C4: I checked my inventory and I already have a couple Panasonic ECG series 47uF 450V snap in electrolytes. I'll use one of those to begin with. If my PT runs exceptionally hot... I can easily replace those with something that's a lower value. The temp issue with the Hammond is a good tip, thanks.

5AR4: I still have a relatively new tube left over from the copper cap install in my ST-120. I haven't experienced any problems not having the delay in B+ on my ST-120, in that amp I'm running Russian made Tung-Sol KT-120's, but the 300B's are a different animal and 4X the price so going with a tube based rectifier makes a lot of sense.

C5: I have a couple Panasonic ECG 150uF 450V caps already in my cart at Digikey. Turns out that's their low ESR line so it's good to see I'm on the right track. I haven't ordered yet so I might get a couple 220uF's as well. I don't think I'll go the external cap route just yet. If I get excessive hum I can always try something else.

C9, C11: Good advice on the coupling caps. The AuriCaps are pricey but I've used them in a previous project with good results so I think that's the route I'll follow.

Speaking of UBT-3's... I'm glad I went ahead and spent the extra cash since OPT's have the most effect on output quality. I'm in the process of repainting them and am having way to much trouble removing the end bells. Turns out that when they were manufactured they used a lot of resin on the screws. So much so that I twisted the head off of one of them trying to get it out. If I was just going to pain them black it wouldn't be an issue but I'm painting the core sating black and the end bells hammertone copper. I've already finished the Hammond and it looks spectacular. Any tips on softening the resin on the screws?

[boywonder]

Originally Posted by OneLiterPeter

The temp issue with the Hammond is a good tip, thanks.


Any tips on softening the resin on the screws?

I believe Russ is referring to the Hammond transformers having a higher output voltage than spec'd, almost as if they are still being spec'd at 115VAC line voltage.........The 200 series may run higher than the 300 series, although I've only played with the 200 series so I really can't speak for the 3XX series.

Check out post number 2 over here: tubelab SE 300b power transformer

For low ESR PS caps, I've been using the Panasonic snap in TS-HA (400V), TS-HB (450V) and TS-UP (500V) series without issue, although as mentioned, there are plenty of choices. My TubelabSE has a 100uf motor run cap installed, and is the best sounding amp I've built to date, but I've only built 3 amps total and the other 2 are PP.

My TubelabSE ended up with a 6uf film cap for C4 IIRC. I'm using the Edcor XPR-131 transformer (thanks Russ for forking out the NRE $$ for that) yeilding a B+ of 360V @ 60ma bias current for the 300B's with 5AR4 rectification. When using an older Hammond 273BX (350-0-350), my B+ was up around 400V.

If you are using a choke (CLC supply), you can dial in (well, reduce anyway) the voltage by reducing the value of C4, that's how I ended up at 6uf.

I have auricaps in one of my other amps and it sounds very nice; I used Wima film caps (MKP type?) in the Tubelab since it uses MOSFET source followers.

Have you tried a heat gun for softening the varnish?

[rknize]

Originally Posted by OneLiterPeter

C4: I checked my inventory and I already have a couple Panasonic ECG series 47uF 450V snap in electrolytes. I'll use one of those to begin with. If my PT runs exceptionally hot... I can easily replace those with something that's a lower value. The temp issue with the Hammond is a good tip, thanks.

Yes, as boywonder mentioned, by "hot" I meant that they are running the core hard and you end up with more B+ voltage than you expect. This translates into a hot (temperature-wise) transformer as well, but that is not the main concern.

Originally Posted by OneLiterPeter

5AR4: I still have a relatively new tube left over from the copper cap install in my ST-120. I haven't experienced any problems not having the delay in B+ on my ST-120, in that amp I'm running Russian made Tung-Sol KT-120's, but the 300B's are a different animal and 4X the price so going with a tube based rectifier makes a lot of sense.

Actually, the 300B is less of a concern. The few seconds of rise time the copper cap would give you is probably enough for the 300B cathode to get hot (being DHT). The input tubes are indirectly-heated, but it's probably not a big deal. I guess for the money, a copper cap is a simple way to get solid-state rectification while retaining the capability of using a tube.

Originally Posted by OneLiterPeter

C5: I have a couple Panasonic ECG 150uF 450V caps already in my cart at Digikey. Turns out that's their low ESR line so it's good to see I'm on the right track. I haven't ordered yet so I might get a couple 220uF's as well. I don't think I'll go the external cap route just yet. If I get excessive hum I can always try something else.

If you look at the PCB, you'll see two circles silk-screened around the cap locations. The inner circle is the diameter of the spec'ed part. The outer is the largest that will fit, roughly. If you go with a bigger cap, be mindful of the diameter.

Originally Posted by OneLiterPeter

C9, C11: Good advice on the coupling caps. The AuriCaps are pricey but I've used them in a previous project with good results so I think that's the route I'll follow.

Yes, they are pricier than they were when they first come out. I had some on hand, so it was less of a concern for me. The Sprague "Orange Drops" are good sounding and very inexpensive...just make sure to get the 716 type. Wima caps are also very good and can be sourced from Mouser last I checked. I haven't tried the latter in the TSE myself. I went from Orange Drops to Russian PIOs to Auricaps in the SSE. I didn't like how the PIOs sounded, but I may not have given them a fair shake. Since I tried them between the Orange Drops and the Auricaps, I can't really comment if there was any difference. The differences tend to be very subtle to me and I only notice them when doing more "serious" listening.

Originally Posted by OneLiterPeter

Speaking of UBT-3's... I'm glad I went ahead and spent the extra cash since OPT's have the most effect on output quality. I'm in the process of repainting them and am having way to much trouble removing the end bells. Turns out that when they were manufactured they used a lot of resin on the screws. So much so that I twisted the head off of one of them trying to get it out. If I was just going to pain them black it wouldn't be an issue but I'm painting the core sating black and the end bells hammertone copper. I've already finished the Hammond and it looks spectacular. Any tips on softening the resin on the screws?

If there are enough exposed threads, I like to run a die up the end of the screw to clear them. Some laquer thinner should soften the coating enough not to bind-up the threads on the nut.

I have UBT-2's in my TSE and am very happy with them.

[OneLiterPeter]

Boywonder...

Thanks for the info and link.

I will check my PT on the bench and see what voltages I get. Then I'll adjust C4 to get to the 350-370V sweet spot.

I'm sure there's a formula that I can use to determine the right cap value and wonder if anyone has one.

[OneLiterPeter]

Russ,

I'll try the 5AR4 first. I have one handy.

As for the the coupling caps... I'm going to order a couple .47 uF 600V Auricaps, I was also considering trying the Jensen Aluminum coupling caps. Do you know if anyone's tried these?

Regarding the transformers, my problem is as follows. I have no problem removing the nuts, in fact they're already off and set aside. The problem I'm having is the during the manufacturing process, a good amount of varnish seeped into the screw holes (approx. 2" deep) and have completely bonded the threads in place. I've been really busy the past few days and haven't had a chance to use my heat gun on the problem, will try that this weekend. I also did some research and found the good ol' turpentine will dissolve varnish. I'll pick up a can from Lowes on the way home and will test it out on the one end bell that I was able to remove and see if it softens the varnish. If it works... I'll drip some in around the threads and see if that won't loosen things up.

Guys, Thanks again for the help.

Pete

[VictoriaGuy]

Cured varnish is pretty tough stuff. If this were my project, I'd use a torch (small flame, or mini-torch) on the exposed end of the bolt to loosen things up.
Do this outdoors or in a very well-ventilated area....
And be careful if you have much turpentine in there, as it is flammable. I'd blow out the turps before messing with flame.

[OneLiterPeter]

This weekend I was able to get the end bells off of the UBT-3's.

On average 2 out of 4 came out without too much effort. a couple I was able to tap (more like hammer) out and one on each I had to drill out. I saved one of the screws to snap a picture of but it'll have to wait until I get home from work.

I also was able to sand and paint the cores and end bells. The cores got painted satin black and the end bells got painted hammertone silver. They still need to dray for a day or two more before I screw everything back together. Will post some pic's once I have them completed.

BTW... Turpentine did not work but it sure did a great job of stinking up my garage. I did contemplate heating up the cores but I figured I'd use that method as a last resort. In the end it all worked out.

Thanks to all for the help

Pete

[boywonder]

Peter: It may be a little late, but sanding the lams on the transformers may not be a good idea, since you run the risk of shorting some laminations.

I have no idea how likely sanding will screw them up; maybe someone with more experience will chime in.........

I leave them as-is, even if they have varnish drips on them, or just paint over the varnish.