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2A3 SE and Edcorp tranny

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#5
Hi Steve,

It would be a waste of the 2A3 with Edcopr OPT. 2A3 is a very good sounding tube that it is worth to match with good quality OPT.

If you want to keep the cost down, get the Hammond 1627SE, or James 2.5K OPT.

My friends and I have good experiences with Hammond and James.


Johnny
 
#6
I agree that the 2A3 can be a good sounding tube, and is often used in expensive amplifiers with expensive transformers. That does not mean that it should not be used in a budget amplifier. You can get Shuguang 2A3's for under $30 each.

The Edcor XSE15-8-5K is a nice sounding transformer and at the 2 watt level it will compare with many of the big boys especially if your speakers are limited to operation above 60 or 70 Hz. For $20 each it is the OPT deal of the moment. Add the $40 Allied 6K56VG power transformer and you can have a relatively good amp for a good price.

I have used these transformers with 2A3's although I am not a 2A3 fan. I prefer the Shuguang 300B. A 5K transformer will work on either tube with slightly reduced power output, but reduced distortion. As mentioned before, run the tube up near its maximum voltage rating at a lower than normal current to take advantage of the 5K load.

I am partial to my amplifier design, but it may be too complex for an inexperienced builder:

http://www.tubelab.com/TubelabSE.htm

It is possible to use the Simple SE circuit with a DHT, but you may need a DC filament supply for the 2A3. I do not yet have the entire schematic on my site, but it will be there in the next few weeks. The PC board schematic can be found here:

http://www.tubelab.com/SimpleSE_schematic.htm

There are dozens of 2A3 schematics on the web. Google around, and find something that you feel is within your abilities.
 
#8
Short answer from experience, most likely yes.

I have heard this transformer up to 5.5 watts with a trioded EL36 (which has a very 2A3 sound) and you can easily get 24 - 19.5KHz with zero NFB at that level. Toss in 3dB NFB for full 20 - 21KHz.

Same great sound from a "little 2A3" (the 45) with extended response.

I've used bias up to 60mA with this transformer with no loss in performance.

I say most likely, because I have yet to hear a genuine 2A3 with it.
 
#9
I have used this transformer with at least a dozen different tubes, including twin plate RCA 2A3's and Shuguang 2A3's. I have never been a 2A3 fan, but they sound very good with these transformers. The frequencies above 200 Hz have as much if not more life to them as transformers costing much more. In the 20 to 80 Hz region this transformer will saturate at powers above 5 watts. This is not a problem at 2A3 power levels.

I run 45's and 2A3's at 325 volts this is way over the line for a 45 and a little over the line for 2A3's. I have not had any issues yet, but YMMV.
 
#10
Thanks to all for the comments and reccomendations.
Tubelab, I'm leaning towards your simple se board since this is really sort of and experiment for me. I'll email you re this.
I would appreciate comments from all on this schematic also . (of course I would like to use my Edcorps txs since they seem like a pretty good fit. (I know theyre not ideal) I'm really trying to get a feel for the sound of a low power SE amp without spending a ton of money.


http://www.angela.com/catalog/how-to/SE.2A3.html


Steve
 
#12
I would second the post above. I prefered the SRPP 6SL7 instead of that 2-stage.

There's a JE Labs 2 stage 6SN7 design, also a Sun Audio 6SN7 (high gain), but given the choice I'd go for the JE Labs 2A3 DX (76/56 as driver tubes).

The SRPP 6SL7 is more on the bright side (emphasized when using Sovtek tubes) and the 6SN7 2 stage is more on the dark side (using the same Sovtek). This is based on my experience building them 2A3 with different octal driver configurations.

Your choice.

ps.

The LF will benefit from a good OPT. I'm using MagneQuest on mine. Haven't tried the Edcors, but would like to give them a try soon.
 
#13
I plan to go ahead with this SE project soon. Just a last thought. I have some used but good EL34s and I'm wondering based on some negativity to the 2a3 if I could use EL34 in triode Single ended instead and with the 5K Edcorp.
Ideas appreciated!!
Tubelab. How do you order one of your boards ? My email doesnt seem to work to your site directly.
Steve
 
#14
I could use EL34 in triode Single ended instead and with the 5K Edcorp.
Click to expand...

Yes, you could do this. The Edcor transformer also has ultralinear taps so that you could try UL mode also. I have a SimpleSE board running with EL34's and a switch to go from UL to triode mode. You can't do this with 2A3's. It has been operated with about 10 different types of output transformers including the Edcor 5K's. The Edcors are the transformers to use in the under $50 each category and the ones that will be used in the amplifier kit that I plan to release later this year.

Tubelab. How do you order one of your boards ? My email doesnt seem to work to your site directly.
Click to expand...

I have heard from some people that they can't e-mail me however these are almost always from e-mail addresses in Asia. My service provider can not find an issue. I have spam filtering that catches most of the BS and occasionally traps a real e-mail. This only happens 2 or 3 times a year.

In your case, I got your e-mail yesterday. I am not allowed to engage in any "activity related to secondary employment" while at work, and I get home from work at about 8PM most evenings (8:30 last night). This leaves e-mail for a weekend only activity. I give priority to e-mail from customers who have purchased a board from us. Those get answered first. I also get about a dozen e-mails a week asking me to design something special, or modify a common circuit, or even suggest how to build an amp. If I answered each one of them completely (which I have been trying to do) I can't keep up. I am about 2 weeks behind answering those e-mails right now. I have been trying to answer most of the common questions on the web site or here in this forum. I get a lot of e-mail questions that have already been answered here. This forum allows the reader to get several opinions instead of just mine. (You already knew that). This can however be confusing to a beginner when there are several conflicting opinions.

As to the boards, there are currently two board designs:

The original TubelabSE is a "no compromizes" SE amplifier design that can use a 45, 2A3, or 300B tube. Most builders have used 45's or 300B's. I know of one user who used 2A3's and eventually switched to 300B's. Most people who build an amp of this nature tend to buy premium tubes and parts (including transformers). Many builders have spent in excess of $1000 on their amplifiers. This board was not intended to be a beginner level amplifier, and should not be someones first vacuum tube construction project, however a few first time tube amp builders have successfully built the amp. All had prior experience with electronics construction. The amplifier requires measurements and adjustments on a live board to set the bias. These adjustments are needed every time the tubes are changed.

The board assembly instructions are posted on my web site. The section of the manual related to assembling the board into an amplifier is still incomplete. This was wiped out when my computer crashed. I had several completed boards that were used to make build amplifiers in the process of making that section of the manual. I sold all of them during the 2 months that my lab was down due to hurricane Wilma. I have built some more boards, and am in the process of shooting all of the final amplifier assembly pictures for both manuals. The remaining sections for the TubelabSE assembly manual will be posted as they are done. Many users have decided that they can build the TubelabSE board from the assembly instructions that are currently posted. I have sent them boards. These transactions have been conducted via e-mail. Feedback from these users has been used to improve the TubelabSE manual, and the SimpleSE manual.

The newest board is the SimpleSE board. It was designed because I received a zillion e-mails requesting a good SE amplifier that didn't cost $1000. The SimpleSE uses 6L6GC's, EL34's, KT88's or 6550's. DHT's can not be readilly used in this board. A tube or solid state rectifier can be used. In can be wired for triode, pentode, or UL mode if your transformers have the tap (Edcors do). This amplifier was designed to be flexible enough so that the simplest version could be built relatively inexpensively. I have built a complete amplifier for under $150 USD. The same circuit board can be used for a higher quality amplifier by adding an external motor run cap, a tube rectifier, and quality output transformers. No changes to the board are required. All off board connections are made with screw terminals.

I am in the process of finishing up the manual. 4 boards have been built, all photos have been shot. Some photos must still be processed for the web. I have started the final assembly of the first complete amplifier. I would expect to have the first cut at the assembly manual done in about two weeks. I will post it to my web site as soon as it is done. I have got my web site set up for simple e-commerce, so there will be an ordering page for both boards on the site. I can not predict my work schedule, or the weather (I need a few hours outside to drill and paint the chassis). This may add another week or two.

Now, I have a question for the people out there with more experience than me in this matter. Demand for the new board is high. Most of the potential customers are not in the USA. I have used the US post office to send TubelabSE boards to Europe and the UK without issue. They are economical, but there is no tracking ability, or proof of delivery. My friends in the kit business will only ship overseas using DHL or Fedex. These carriers charge $30 USD to deliver a PC board. They claim that too many of their kits never arrived in Asia, or the customer claimed that the never arrived in order to demand another kit. There is no way to tell which happened.

Anyone with experience here? Is there an alternative to use in areas with high fraud rates?
 
#15
I built the JE Labs Simple 45/2A3 (http://members.myactv.net/~je2a3/simple45.htm) with the Edcor transformer in question. It sounds fantastic - plenty of upper extension, sweet mids and deep, tight bass. I did scrap the original design's power supply, replacing it with a CLCRC arrangement. I've also replaced the 5Y3 with a 5AR4. I'm running vintage 45s; haven't tried 2A3s, though I understand that the Sovteks sound great at the 45 operating point.

Any day now I'll get around to upgrading the Orange Drops to Jensen copper PIOs. Before that, though, I'll replace the R in the ps with the 10H choke that arrived yesterday to see if I can discern a difference hum-wise (not that it's audible more than 6" from the speaker).

I'm sure I'll eventually break down and spring for the James transformers as others have suggested, but for now there's still some tweaking to do. I conciously chose the Edcors as a jumping off point, as I was unfamiliar with SETs and was afraid to spend that much up front. Basically, this amp was (and still is) an experiment - a work in progress - and now I know that it's a path I'm willing (dying!) to pursue.

FWIW, I'm running straight into Fostex FE206Es (96dB @ 1W/1m). How efficient are your speakers?
 
#16
I kinda like the idea of the strapped EL34 with a 6SL7 up front. I'm running that combo into a 10K primary (for low distortion) but you could make a bit more power with the 5K. On the 2A3 plate voltage, I'm running about 335v SE on some RCA dual plates, with no problems to date.
 
#17
Tubelab,
I have heard from some people that they can't e-mail me however these are almost always from e-mail addresses in Asia. My service provider can not find an issue. I have spam filtering that catches most of the BS and occasionally traps a real e-mail. This only happens 2 or 3 times a year.
Click to expand...
In your case, I got your e-mail yesterday.
Click to expand...

OK, This explains it. The ones I sent from my other house on the weekend were probably the one that came back meaning it's that service provider.
I'll keep and eye on your site for that simple SE board info. Thanks

They claim that too many of their kits never arrived in Asia, or the customer claimed that the never arrived in order to demand another kit. There is no way to tell which happened.
Click to expand...

I used to sell CDs and stuff on ebay and had the same problem. I gave the option of shipping methods and the cheap overseas method offered no warranty of delivery. I just kept a copy of the mailing receipt from the post office which shows most of the destination info etc. This helped. On ebay however, I had the benefit of seeing the buyers feedback and that helps weed out alot of the crooks. BTW, don't take Paypal payment unless you have delivery confirmation. The buyer can request Paypal to refund his money and they will, unless the seller has ONLINE VERIFIABLE DELIVERY CONFIRMATION.
Triode recently began selling on ebay and they have a good sized ebay store.

Beeah,
I would probably use some Infinity RE Ones I have which are only 89 db I think. If I like the sound of the design I used for this experimental amp, then I'll build an enclosure for it and a proper chassis etc. I was considering those speakers you have in a small bookshelf 2 cu. ft. homemade enclosure.
 
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