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PostPosted: 27 Aug 2018, 11:49 
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Joined: 24 Oct 2010, 07:05
Posts: 282
There are so many tube testers to check the EL34.
You can check the amp with a resistor in place of LM317. Not sure if it is a cheaper option.


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PostPosted: 27 Aug 2018, 15:54 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi. yes you can test with a resistor. For a quick test a 250 ohm 5watt will be OK (30 volts on the cathodes at 125 ma for the pair). It wont sound as nice but will work

Good listening
Bruce

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PostPosted: 02 Sep 2018, 02:57 
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Hello Bruce!

I have a question. A guy posted in an other forum about a question regarding the Oddblocks.. I could not answer it, but I am really interested in your opinions.

Is this transformer could replace the edcor ones?

https://sklep.toroidy.pl/en_US/p/TTG-EL84PP-Tube-output-transformer-8kOhm-2xEL84-Push-pull-or-similar/561

Thanks for your help


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PostPosted: 03 Sep 2018, 10:33 
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Hi, I saw the question and chuckled at some of the responses...if all I cared about was max power then I would not use an Oddwatt design. It is inefficient, true, all class A amps are. I avoided jumping in as I saw no purpose. The folks that didn't understand what the design was based on (common as it is different) did not understand forced class A push-pull designs and how it operates. They presume it will have inferior performance. Sorry to disappoint them. None the less, yes that transformer ought to work. And while the folks didn't seem to like Edcor trannies, they do what is needed and are cost effective. High priced others will not do significantly better IMO. With hundreds of happy builders (and buyers of the commercial versions) I rest my case.

Good listening
Bruce

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PostPosted: 03 Sep 2018, 11:24 
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Joined: 02 Mar 2009, 12:41
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Location: Vänersborg, Sweden
For us Europeans, buying from shops across the pool (the Atlantic ocean) is a p*** in the a**. Shipping is often as much as the goods and add to the (the Swedish) VAT/sales tax at 25% that works on the WHOLE SUM (=goods+shipping+package+insurance+bribes to the guy who took the parcel to the UPS office ...).
I love Edcore and I love Hammond, but Edcore closed its office in Belgium. The Polish place referred to is a good alternative as their quality and price are OK.

However this wasn't my main point. I did see a preamp on diyaudio.com (or was in here??) using some really nice tubes.

Found something like them on http://www.vt4c.com and remembered I had something yet more strange somewhere else.

Heres the 6SN7 with blue glass: 8-)

Image

However, they are just $250/pair ... :eek:

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“If you don't know where you are going, any road will get you there.”
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PostPosted: 03 Sep 2018, 13:02 
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Joined: 31 Aug 2018, 09:13
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Thanks Bruce for the informations!

Yes, I was also stunned by the people over that forum... while not giving a clear answer, they started providing schematics to other designs..

I got excited about building an Oddwatt myself too in the process of getting the information! :)

Thanks
Sebastian


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PostPosted: 07 Sep 2018, 02:36 
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Joined: 09 Aug 2018, 03:15
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Location: Forsbacka Sweden
Sins i live in Sweden. Just 1hour away from Lundahl transformers factory. Is there for any chance possible to replace the Edcor Cxpp25-ms-8K with one of Lundahls? I don’t find any with 8K impedance but there are several that might work. Maybe LL1679 https://www.lundahltransformers.com/wp- ... s/1679.pdf or other with minor changes in output stage?
And if it’s possible. What changes need to be done? :idea:
I’m really into this now and have used Lundahls before. And they are great performers if used right...
Yes I did see the conversation above and I agree with Bruce and the other Swede (Soundbrigade). Just want to clarify as much as possible before I proceed. And I have concidered the Polish iron also sins its reachable for me. Im used to buy chokes from Poland (Toroidy) and they work really well.
Im looking forward to get help and choose something suitable.

Regards Kalle G

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PostPosted: 07 Sep 2018, 15:00 
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I'd better use slightly less impedance than 8k, lets say 6.5k.
There should be no change necessary.


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PostPosted: 07 Sep 2018, 16:25 
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Hi, It is a question of (a) what output tubes you plan to use and (b) do you want to maximize power or lower distortion. For higher power the lower impedance transformer will be fine. With KT88s the change in distortion will be slight and unless you have test gear (like the distortion analyzer I have) not likely to be noticed. Output will be higher, but not a lot. With EL34s, 6CA7s, and KT77s the higher impedance would likely be my choice. The loss in power would be slight and the distortion lower, again without test gear not noticeable. The design is quite flexible and tolerant of output impedance changes. Surprisingly large deviations work well. The best ones IMO for an amp that can use both the EL34 type types and KT88s is 8K. To select only one I would likely drop the impedance to about 7200 for KT88s only and raise it to about 8500 for the smaller tubes. If you look at the KT120 version it can use KT88s with an impedance of either 3600 or 4200. Performance is quite good there as well. I suspect it is partly do to the massive amount of iron in those trannies though (each is about 5kg). The design being full time class A operation is different from more typical class AB ones and the values given above are not suitable for AB operation. They would throttle such an amp severely.

A curious add on.... If you set the amp for 8K (all mine are) and the lower power range (about 62ma per tube) and use KT120s the result is really nice. A small amount of higher output (nearly 20 watts) than the El34s etc and what seems to be a more robust (if that is possible) sound. I presently use a quad of such amps in my system (it is bi-amped with the subs set for 45HZ crossover). A good friend of mine thinks that all big bottle tubes sound better than skinny ones. It might be that simple. However my experience with KT120s has been that they have a really clean sound regardless of how they are used.

Good listening
Bruce
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PostPosted: 08 Sep 2018, 02:42 
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Joined: 09 Dec 2013, 01:11
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Location: Canada
ForsbackaKalle wrote:
Sins i live in Sweden. Just 1hour away from Lundahl transformers factory. Is there for any chance possible to replace the Edcor Cxpp25-ms-8K with one of Lundahls?


Hi,
I replaced this exact Edcor with Lundahl LL1682/PP and I think it sounds better with KT77. It's also better wound transformer, with higher self-resonance frequency, and the general feeling is of superior quality. One inconvenience though - only one output option (5.5 ohms). However, considering how the output taps are taken in the cheaper transformers it's probably better like that.
My problem with the Edcor was that it had 30% difference between the two halves of the primaries. That only tells me that it's wound with too many compromises to keep the prices so low.
Regards


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