• Disclaimer: This Vendor's Forum is a paid-for commercial area. Unlike the rest of diyAudio, the Vendor has complete control of what may or may not be posted in this forum. If you wish to discuss technical matters outside the bounds of what is permitted by the Vendor, please use the non-commercial areas of diyAudio to do so.

Joining the Tubelab SE club

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
PaulyT said:
I really can't judge whether the power would be sufficient... I'm guessing not, hence my interest in the 300B. But you've got me at least considering the 45 as an alternative.

Really depends on the sensitivity of those horns. The TSE with 45s can fully drive my 98dB speakers to uncomfortable volume levels without difficulty. They work well for "critical" listening by myself, but are lacking when I want to rock and roll. I now have a working SSE for that.
 
PaulyT said:

2) The power transformer, guess Hammond 276X is still a good choice? Never shopped for transformers before, so I have no idea what alternatives there are...


4) Will do the R4 choke mod - is the Triad C-14X still the way to go here?

5) For the supplementary cap at C5, docs say "I added a large 100 uF, 370 volt AC polypropylene motor RUN cap to my 300B amp." Anyone know where to find one of these? Not sure if digikey sells them, mouser seems to go up only to 80 uF in this class... (and wow, these aren't cheap!)
2) Go with Edcor or Electra-Print. I've tried a few Hammond power t and I personally cannot recommend it.
4) Yes, especially for high efficiency speakers.
5) ebay has good number of listing (at least when I looked).

Here's a tip I posted on dealing with input tube socket.
 
Haven't heard back from Edcor. I'm working with Jack from Electra-Print on a quote for a set of three transformers, two output and one power. Here's what I'm looking at:

2 x OPT: 5k, 100ma to 6 ohms ($125 ea.)

1 x power: 660vct @ 150ma, 5v @ 3a, 6.3v @ 5a ($141)

Before I pull the trigger, does this seem reasonable for what I'm building? I know I don't necessarily need the full power for driving just HF horns, but I'd rather build a more general amp just in case (like if plans change or I want to sell it someday). And yes EP is a little more $$ but this is my first amp and I'd rather get something known to be solid and dependable, rather than experiment with cheaper (or more expensive and "esoteric") stuff right now.
 
Making progress, got the tubes ordered, and will probably order the EP transformers tomorrow.

Working through some of the other parts, I notice that C9,11 are .22uF caps in the schematic/specs, but the AES part # is actually a .47uF... and seems to be the same as what's pictured in at least one of the images in George's instructions. How do I decide what cap to use here? Should I just go with the .47 from AES?
 
agent.5 said:



You may want to wait for a response from tubelab before you order the transformers. I think you want the OT to be gapped to 60ma instead of 100ma.


I'm confused, I thought the gapping affected the voltage, and the amp rating was simply the max current it could handle? For example, the UBT-2 is 5k primary, 4/8/16 secondary, with 110mA max current. That's pretty close to the OPT specs I posted.

?
 
PaulyT said:



I'm confused, I thought the gapping affected the voltage, and the amp rating was simply the max current it could handle? For example, the UBT-2 is 5k primary, 4/8/16 secondary, with 110mA max current. That's pretty close to the OPT specs I posted.

?


gapping only affect the current and operating point of the output tube. If you 300B is operating at 60ma, you want the gap to be 60ma. You always want the gap to be as small as possible. In fact, when it comes to OT, size does matter. The smaller the better, for the core size and gap size.
 
PaulyT said:
Well, then I have no idea how to spec this out, then... because George doesn't talk about the current rating on the OPT at all.

:xeye:


Just PM or send him an email. He did say the following in his prior post, and it is why I said that you may only need a 60ma gap:

"At any rate these are very good transformers (possibly the best that I have used). The specs were a single ended OPT gapped for about 60 mA (a compromize between 45's and 300B's) rated for 10 watts with a 5K primary impedance and a single 8 ohm secondary impedance. Other impedances to match your speakers were available. Mine still live happily in my Lexan amp visible on the Tubelab home page."
 
PaulyT said:
Making progress, got the tubes ordered, and will probably order the EP transformers tomorrow.

Working through some of the other parts, I notice that C9,11 are .22uF caps in the schematic/specs, but the AES part # is actually a .47uF... and seems to be the same as what's pictured in at least one of the images in George's instructions. How do I decide what cap to use here? Should I just go with the .47 from AES?

Anything over 0.1uF should suffice. This amp has no feedback loop, so the value isn't terribly critical so long as you don't go too low and have to deal with HF roll-off due to the FET bias circuit. 0.22uF is a good value to use here but 0.47uF will also work fine. Smaller caps are cheaper and theoretically sound more "transparent" (since there is less of it).
 
agent.5 said:



Just PM or send him an email. He did say the following in his prior post, and it is why I said that you may only need a 60ma gap:

"At any rate these are very good transformers (possibly the best that I have used). The specs were a single ended OPT gapped for about 60 mA (a compromize between 45's and 300B's) rated for 10 watts with a 5K primary impedance and a single 8 ohm secondary impedance. Other impedances to match your speakers were available. Mine still live happily in my Lexan amp visible on the Tubelab home page."


No worries, I'm not in a rush; I'll wait to see if George responds to this thread, will ping him if he doesn't. Meanwhile I'll do some more research to try to learn more about what exactly the gapping is and what effect it has in this sort of circuit. This is all a big learning experience for me anyway...
 
I think you want the OT to be gapped to 60ma instead of 100ma...... 2 x OPT: 5k, 100ma to 6 ohms ($125 ea.)

The gap in a single ended OPT is added to eliminate core saturation that is caused by the DC current flowing through the transformer. The gap is usually optimized for the amount of current flowing which is the same as the bias current. You adjust this to a particular value when you set up the amp.

The range of allowable values is determined by the type of tube being used and the voltage applied to it. The 300B tube has a maximum rating af 100mA. It requires at least 40 mA to be in the linear part of its operating range. Therefore it would be acceptable to adjust the bias on a 300B tube to any current in this range. The operating current will affect the sound of the tube, and most people feel that the 300B sounds best in the 60 to 80 mA range.

The 45 works best in the 25 to 30 mA range.

The gap is optimized for a given operating current but the transformer will operate over a fairly wide range especially below the specified rating.

The world of output transformers and their specs is cloudy at best and often full of some serious BS especially with respect to the power ratings of some OPT's, like the "50 watt" ones sold on Ebay. Some manufacturers like One Electron specify a maximum current. This is the point where the gap will no longer control the saturation and the power handling capability of the transformer starts to drop quickly.

I am not sure how Jack specifies his transformers. I would tell him that you want to run 300B's at 70 mA or so, and be able to run 45's as well. He knows far more about OPT's than I ever will, especially HIS OPT's since he makes them! The OPT is the most important component in a tube amp, especially in a SE tube amp.

When Albert ordered the original pair, our priorities were the other way around. We wanted to run 45's primarilly, and be able to run 300B's or 2A3's in the same amp, but at less than the "normal" current since the power transformer we used ran the bigger tubes at a lower voltage than they really wanted. Jack suggested the 60 mA compromize and it works very well with 45's at 30 mA.

I still use 45's in that amp 90% of the time even though I am using Yamaha studio monitor speakers that have a 87db rating. It is not loud but plenty adequate in my small 10 X 11 foot room.

I notice that C9,11 are .22uF caps in the schematic/specs, but the AES part # is actually a .47uF.....Anything over 0.1uF should suffice.

Indeed just about any value from .1 to 1uF works fine and I have used .1, .22, .47, .68 and 1uF in my amps based on whetever I can find for a reasonable price. My latest amps have .22uF's in them. I used .47 for a while because AES offered me a bunch for a special price. I have even used 1uF because I got a big bag of Wonder Caps on Ebay.

1 x power: 660vct @ 150ma, 5v @ 3a, 6.3v @ 5a ($141)..... does this seem reasonable for what I'm building?

The actual current will be slightly over 150 mA so I would opt for a bigger current rating like 200 mA. Each 300B will draw from 60 to 80 mA based on how you set it up. Each 5842 will draw about 10 mA. The other circuits on the board (mosfets, bleeder resistor, etc) draw about 20 mA. The total can be 160 to 200 mA.

This would make the Electra Print a rather expensive power transformer. The Edcor may be a better choice for cost reasons alone. The power transformer is not a major player in the sound quality of a SE amp, IF it is built correctly.

I have always used Hammond or surplus power transformers in my amps for cost reasons. I still have some Hammond's in my stock and I intend to use them, They are all about 5 years old. The quality of their recent production has been seriously questioned. Their have been numerous reports of mechanical buzzing from recently built Hammond transformers.

I am sure that Jack builds a good (but somewhat expensive) power transformer. I have heard good reports from users of Edcor power transformers and the version speced by Rknize will work in your application. I have not used either Edcor or Electra Print power transformers, but I have used their OPT's and find them both good. OPT's are much harder to get right since they must cover a wide range of frequencies. I plan to buy an "Rknize" Edcor power transformer when the budget allows, but I have spent over 3K on PC boards so far this year, so It won't be soon.
 
Hmm...I hope this transformer works OK for everyone now that my user name is associated with it. :eek:

One little tidbit about this transformer: the core laminations are exactly the same size as the Hammond 193J choke. I found this out because I removed the bells off of my choke so that I could fit it under the chassis (there is a lot of wasted space in there). They mount on the Edcor perfectly. The EP transformers look to be a similar style as the Hammond, so if you want them to look more consistent, that is an option....

I switched them because I wanted the side knock-outs on the Hammond bells and couldn't bring myself to drill holes in those nice blue ones. Maybe I'll use the blue Edcor bells on a Hammond choke on some future amp....
 
PaulyT said:
Quick question: I don't plan to put a volume control in the amp (controlled by the preamp), so do I simply hook up the input lines to L2/R2? (Or, equivalently, jumper L2-L3 and R2-R3... but that's just more soldering.)
For your active bi-amp setup, you want to have a volume control in your TSE. Especially with high efficiency speakers it's required in order to keep the noise floor down.
 
Well, I will effectively have some sort of volume/level control in the line before the TSE, I just don't want to have to use a knob on the amp itself when I want to adjust the relative balance of the LF and HF. It's too easy for it to get changed accidentally (especially since I have 2 and 5 yr old kids who are very curious). I figure I'll have some little box with a couple internal pots in it between the crossover and the LF and HF amps and sub. Will likely have some simple eq. circuitry in the same box to adjust the overall response across the different drivers.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.