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 Post subject: Re: KT120 Oddblocks
PostPosted: 26 Mar 2011, 06:04 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
Soundbrigade wrote:
BASTARDS!!!!!

Just because you wrote about this tube, I simply had to order me a pair and try it out myself ... :x

Magnus, you're priceless! :D

Quote:
Been looking at this schematic.

Meh, my 845 kicks that ;)
(pro'lly not on price though :blush: )

Cheers!

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 Post subject: Re: KT120 Oddblocks
PostPosted: 26 Mar 2011, 06:20 
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Joined: 30 Apr 2009, 22:36
Posts: 24
Location: Australia
For power transformer, try the Edcor XPWR117-120/240

Power transformer for a 120V or 240V, 50/60Hz. line to 360V (180-0-180) at 500mA center tapped and 12V at 6A. Approx USD77.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 26 Mar 2011, 07:32 
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Joined: 02 Mar 2009, 12:41
Posts: 1051
Location: Vänersborg, Sweden
I have two transformers 350V @ 200mA, 6,3V @ 5A, two chassis and two Hammond 1627 trannies. I have to wire the OP transformers for 4 Ohm and load them with 8 Ohm to get my 5K anode load. Not very nice behaviour but still a way to go.

If this won't work another way is to use Edcor CXSE25-8-5K transformer.

Also I want to use floating bias as I have no bias tap on the transformer.

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 Post subject: Re: KT120 Oddblocks
PostPosted: 26 Mar 2011, 16:09 
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Joined: 04 Jun 2008, 20:59
Posts: 3749
Location: Arizona, USA
Hi All, The tube is as noted about a year old. And obviously no NOS. Right at present I'm using Edcor CXPP60 watt output and a XPWR023 for power. It is a bit on the light side but will deliver just over 400ma at 400 B+ with solid state rectifiers. I would like about 50-75 more B+ and then could lighten up the current a bit. You have to watch that as you can exceed the tube dissipation with numbers in this area. :firefighter: My present thinking is that 3600 ohm load may be better than the 4200 of the existing CXPPs. Before everyone jumps all over me, I have not found the models to work well with these tubes.

Yes I do believe they would be awesome in a guitar amp. My initial listening indicates a lot of bottom end and in AB pentode mode you might get over 150 watts a pair before things went south.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 26 Mar 2011, 19:17 
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Joined: 06 Jun 2008, 18:23
Posts: 4918
Location: Australia
Soundbrigade: you have to blame Bruce for the exposure to the KT120. I reacted exactly the same as you. Bruce anounced the tube and I orderd two matched pairs straight away. What I did for a quick and dirty listen was to use Mikael Abdellah's Single-Ended (SE) KT88 / 6550 Tube Amplifier Schematic and dropped the K120 in place of the KT88 tubes. Then kept dropping the cathode resistor to push more current through the tube. Here are my Tung-Sol KT120 Tube SE (single ended) listening Impressions.

This worked in a fashion. I got a couple more watts out of the amp and a chance to listen to these new big tubes. Where it fell apart was the power tranni gets far too hot and the low end OPTs saturate because of the high idle current. But I was able to get a glimps of how these tubes will sound. The amp was the Be Bamp (bread board amp). The whole build got really interesting is where I added interchangeable driver stages (6N1P and 6SN7).

The plan is to build a better specced amp around these tubes. As Bruce has pointed out with two tubes (pushed) you could get 150W a channel. You are talking big power.

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 Post subject: Re: KT120 Oddblocks
PostPosted: 27 Mar 2011, 02:59 
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Joined: 02 Mar 2009, 12:41
Posts: 1051
Location: Vänersborg, Sweden
I did try the very little slighter smaller EL156 using the 6E5P - Rusian tetrodes). I had some figures how to bias the EL156 but I guess that the transformers' Ra was to small and the power transformers (I used two in a pseudo monoblock) were a bit underrated and ran very hot.
The amplifier sang however (until I, at a DIY-meeting, dropped one tube 3" on a hard surface :tombstone: ) and it seemed to work pretty OK.
I was a bit intrigued by the heavy tubes the EL156 were and now the KT120 and have an urge to get me some pretty singel end amplifier with a considerable output power. My other amps with 6AQ5, 2A3, 5998 etc are small. Even the 5998PSEhas a limited 7-8W which is not enough for most speakers.

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 Post subject: Re: KT120 Oddblocks
PostPosted: 29 Mar 2011, 03:08 
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Joined: 24 Oct 2010, 07:05
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gofar99 wrote:
... deliver just over 400ma at 400 B+ ... I would like about 50-75 more B+ and then could lighten up the current a bit. ... My present thinking is that 3600 ohm load may be better than the 4200 of the existing CXPPs.

Do you mean 3600 Ohm each side or total (2x1800 Ohm)? It seems that with increasing B+ the tube likes more load (more resistance), but my weekend tryings showed that the results is very inconsistent. :( Maybe just my mistake somewhere in the circuit.


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 Post subject: Re: KT120 Oddblocks
PostPosted: 29 Mar 2011, 15:42 
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Joined: 04 Jun 2008, 20:59
Posts: 3749
Location: Arizona, USA
Hi, All my fault (sob).. :bawling: ... In AB a pair of KT120s ought to be stunning and if they keep the same sonic signature (as in the class A amps) the bottom end should put fear in everyone's hearts. I was listening to them this weekend and they are beasts - but very nice beasts. I have the last batch of changes to try and hope to do that this week. Then I'll post the results and basic schematic. In class A the 60 watt Edcors seem fine, for AB the 100s are a must. In either case the power trannie needs to be in the 200VA class. More would be better. A target B+ of 475 V at 300ma continuous with at least 50% reserve and lots of heater power. The heat sinks I found have a rating of 2.6 degrees C per watt and seem to be just fine with the LM317HVs. Garden variety ones will not cut it.

Sorry for the delay in getting this one on the forum. I'm busy getting stuff ready for an Audio Fest in Dallas about 6 weeks from now.

Good listening
Bruce

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 Post subject: Re: KT120 Oddblocks
PostPosted: 30 Mar 2011, 05:36 
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Joined: 02 Mar 2009, 12:41
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Location: Vänersborg, Sweden
I heard an advice "like drives like" = triode drivers for triode powertubes, pentode drivers for pentode OP tubes etc.

Could I use an EL84 or 6AQ5 or even a 6V6 for the KT120?

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 Post subject: Re: KT120 Oddblocks
PostPosted: 31 Mar 2011, 15:27 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, An interesting topic that crops up from time to time. My sense (and apparently many of the commercial high end companies) is that it really doesn't seem to matter. I could easily argue either side of the question. My personal thoughts are that if you have different drivers and outputs it might be better. You would have 2 different kinds of distortion that might not be additive, but with both the same they could be the same and end up more audible. :2c: Like I said I don't know that it matters. Anyone have some good info on this??

Good listening
Bruce

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