Halving OPT's pri.imp. by connecting 8ohm load to 16ohm tap - Good/Bad? - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 17th May 2005, 09:56 AM   #1
argo is offline argo  Estonia
diyAudio Member
 
Join Date: Feb 2001
Location: Estonia
Default Halving OPT's pri.imp. by connecting 8ohm load to 16ohm tap - Good/Bad?

Sorry if the topic is already covered somewhere but just couldn’t find it.
Being a bit cheapskate here, I am wondering what would be the penalties (performance, output power, sonic wise...etc.) if trying to halve the OPT's primary impedance by connecting 8ohm load to 16ohm tap?

argo
  Reply With Quote
Old 17th May 2005, 10:19 AM   #2
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
Loss increases, and damping factor drops slightly if not using gNFB. Bandwidth is about twice as wide (if not necessarily at high power, low frequency).

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 17th May 2005, 10:35 AM   #3
argo is offline argo  Estonia
diyAudio Member
 
Join Date: Feb 2001
Location: Estonia
Oops, I forgot to mention – for SE amp
It has been difficult to locate/obtain a good SE OPT for 6C33C which requires 600 to 800 ohm primary impedance. Now I thought, if for an example using One Electron's UBT-1 (1600ohm pri) in this configuration (which should make 800ohm pri.?) for 6C33C SE amp with, lets say 300V plate voltage and 150mA on tube , how much power and low frequency extension will be sacrificed. Can you predict approximately how much the damping factor would decrease without using gNFB.

regards,

argo
  Reply With Quote
Old 17th May 2005, 12:39 PM   #4
diyAudio Member
 
Alain Dupont's Avatar
 
Join Date: Sep 2003
Location: Paris - France
Argo,

>> Oops, I forgot to mention for SE amp
>> It has been difficult to locate/obtain a good SE OPT for 6C33C which
>> requires 600 to 800 ohm primary impedance. Now I thought, if for an >> example using One Electron's UBT-1 (1600ohm pri) in this configuration >>(which should make 800ohm pri.?) for 6C33C SE amp with, lets say
>> 300V plate voltage and 150mA on tube , how much power and low
>> frequency extension will be sacrificed. Can you predict approximately
>> how much the damping factor would decrease without using gNFB.

It's a good combination I already seen schematics with Hammond OPT 1640 SE and I have asked them about this, "it's allright" lower power output, wider bandwidth ; but a little less bass for that you need current...
And don't go to 300 volts keep it at 250/280volts

I have found these:
http://www.thlaudio.com/indexE.htm

PS: I am building a SE 6C33C-B myself..

Regards.

Alain.
  Reply With Quote
Old 17th May 2005, 01:01 PM   #5
argo is offline argo  Estonia
diyAudio Member
 
Join Date: Feb 2001
Location: Estonia
Alain,
thanks for the input.
Why not 300V?
The UBT-1 is for 160mA max DC. 160mA and 280V comes out aprox. 45W disipation. Not bad but why to limit to this figure?

I try to avoid Hammond like the plague. If their OPTs are built twice as good as their mains and chokes I wouldn’t still consider them as good buy.

Not long I go bombarded thlaudio with e-mails for price request on James opt but they never answered back.
How much did you pay for yours if it’s not secret?

argo
  Reply With Quote
Old 17th May 2005, 03:02 PM   #6
diyAudio Member
 
Alastair E's Avatar
 
Join Date: Feb 2004
Location: South Wales
Default 6C33c O/P Tx

Im in the process of doing exactly the same, SE 6c33c but Ive wound my own Tx with the help of Yves, and his calc from this Forum.

Its easy enough to get the parts for a Tx. and winding although tedious is achievable by hand--Ive got a hand-winder, but it has a few problems that Ive not sorted yet so had to resort to doing it by hand.

Took around 5 hours in all, tested it last night, and sounds quite good. If you decide to 'Roll Your Own' I can let you have the details and turns etc.

Im using Cathode Bias, with 320 odd volts, dropping 90 odd over cathode resistor Anode Dissipation in the regeon of 43W
I chose Cathode Bias, as the 6C33C likes to change its charateristics over a long period of burn-in, and I wanted an amp that doesnt involve fiddling with the bias every couple of hours!
__________________
Das Beste Oder Nichts
  Reply With Quote
Old 17th May 2005, 03:19 PM   #7
diyAudio Member
 
Alain Dupont's Avatar
 
Join Date: Sep 2003
Location: Paris - France
Argo,

Well I dont know anything about Hammond quality production.
But I have seen a schematic for 6C33C-B with a 1640 SE connecting the 16 ohms for 8 ohms output. {And have asked their tech support about it}

I will pay a total of: NT$11026 ~ 447.00 Canadian Dollar
for the 2*James 6130H including shipping .... {I'll tell you about the custom taxes when received}
The base price is NT$7400 for the pair.
It was the best price I had for SE OPT's for 1* 6C33C-B ; otherwise
I got around 400 to 500 US $ for the pair and had to add the shipping charges + customs taxes {Lundahl, etc , even custom made in USA}
I have asked for price to a total of 10 companies for a SE Opt

Mine are shipped today, it took at least 1.5 month after the order
and they don't quickly respond to emails, I ordered on 29 march and expect have the OPT's in 2 weeks... not fast!

For the 300 volts as I remember, from schematic I have seen B+ is between 190 to 270 volts ; I am working on the Simplex from Ari Polisois
he recommends not going over 270 volts in SE ; about the same with
Erno Borbely ... Ari is on line called: G.Cesar in the tube forum
he is active in:
http://www.diyaudio.com/forums showthread.php?s=&threadid=57071

I think he will be able to answer about this point ; he has built several SE
with 1 or 3 * 6C33C-B all published in AudioXpress magazine
.
http://www.valvediy.com/simplexpg1.html
http://www.borbelyaudio.com/special_articles.asp
{there is a glitch in the link http://www.borbelyaudio.com/adobe/15wse.pdf}

I am waiting now for 2 power supply 350 VA toroids to have all components
to make a integrated stereo SE 2*20 watts with 6C33C-B tubes.

I raise a warning, it's a costly amplifier if you want to build one.

Feel free to ask if you need anything.

Best regards.

Alain.
  Reply With Quote
Old 17th May 2005, 03:44 PM   #8
diyAudio Member
 
Alastair E's Avatar
 
Join Date: Feb 2004
Location: South Wales
Default Costly!

If you get really esoteric, there are silver-wire versions available costing literally thousands each!

(doubt if they sound that much better than a good copper version!)

I chose the cheapskate route and rolled my own!

Total Cost for three very large, custom wound transformers,--Less than $50!
__________________
Das Beste Oder Nichts
  Reply With Quote
Old 17th May 2005, 07:49 PM   #9
argo is offline argo  Estonia
diyAudio Member
 
Join Date: Feb 2001
Location: Estonia
Alastair,
I am happy for you, that you got all the Tx parts and even a winder. I have not been so lucky till now. I have been looking for lams and bobbins locally without much success. The best I have found so far is RSComponents selling a 200VA power transformer kit for about 70 euros. I called a commercial tube amp maker here today and asked for some laminations.He promised to look something suitably big but he wasn’t sure at all, if he can find them. We'll see. I will definitely be glad for your and Yves's help in providing the details of your OPTs.

Alain, I think I have seen that schematic with Hammond 1640SE as well and that’s why I asked for some kind of confirmation to the idea or possible pitfalls of this approach.
I have bought some Hammond chokes and power Txs and they were really lousy made ones. I don’t know about their OPTs, though I have read in several places an opinion of One Electrons sounding much better, than Hammonds for the same amount of money. It would be also interesting to hear from you, what the Hammond's tech support guys answered to you about using 16ohm tap instead 8ohm to lower the load impedance.
You got a good deal from thlaudio with these James. I checked for the price of the same OPTs as yours from another supplier in Asia and while the initial price was attractive, with shipping and customs added, it would have turned out as much as buying from Borbely Audio for an example. Lundahl doesn’t make OPTs for this impedance higher than 90mA, if I remember correctly? Did you ask them for custom tranny? It would be closest place to order from them and they are quite reputable quality makers.
You are right about the plate voltage -I checked the datasheet again and it says - no more than 250V if over ran over 30Watts. I must have remembered incorrectly. Well it seems, that the One Electron’s UBT-1 is out. At the end, it's a quite small tranny anyhow - about 2,5 kg.
I kind a like Ari's “Simplex”, especially the direct coupled driver but I am not sure, if will I go with the modulated bias of the output tube though. Because after all, it still has at least one capacitor in the signal path (if not two). And high voltage, an 1000uF electrolytic one ,which would be difficult to find of “Audio quality”. You see, the output tube doesn’t have a current path other way around, than to go through these big elcos. How does it affect sound, I have no authority to say, having not heard one at first.

I have also seen the Borbely's design and liked it very much first. Now, after reading more about the virtues of the SE triode amp’s characteristic harmonic distortion pattern and it's influence on a sound in several places, I have came into conclusion, that using a distortion cancellation mechanism and/or NFB, would defeat the purpose of using SE triode output at the first place
I am considering a fixed bias BUT ONLY with the regulated PS, using another 6C33C as a regulator tube - the dang thing was made for that, why not use it for the purpose!

I have the output tubes, sockets and multitude of driver tubes at hand to choose, some power trafos, chokes, caps, bolts and nuts etc., only if I could get some decent output transformers for not going broke. Alastair's "Rolling Roll Your Own" idea seems tempting one, if proper laminations could be found. It will be long-time, more of an experimenting project anyhow.
As to the cost warning, you are most welcome. I need to keep myself on the budget for not paying outrageously high prices for the OPTs just for the "Big Brand Name's" sake and I have yet to finish my 6AS7 PP amp and the high efficiency speaker pair project going on for too long time.

I am eagerly waiting your and Alastair report on the amps you are making.

Cheers,

Argo
  Reply With Quote
Old 18th May 2005, 09:58 AM   #10
panos29 is offline panos29  Greece
diyAudio Member
 
panos29's Avatar
 
Join Date: Dec 2001
Location: ATHENS, GREECE
Send a message via ICQ to panos29 Send a message via Yahoo to panos29
I am in the same route as you guys but with one difference, I have it ready in my home as we speak, its a simple 6C33SE with Hammond 1640SE wired for 16Ohms and I can assure you it sounds marvelous. The design is based on 6N1P-ECC99-6C33.
the voltage is 220VDC at 200mA. The power supply is CLC. The sound is the best I have heard till now very dynamic, detailed and "human". I have to admit my speakers are 100dB sensitive(tannoy monitor gold horn loaded). The amp belongs to a friend and got it for audition now. Mine just started and will be exactly the same but with anoter 6C33 as a power supply regulator for both channels(already tried and sounwise is excellent).

The amp design can be found here:
http://audio.dynatech.gr/toppage4.htm

The speakers:
http://audio.dynatech.gr/horny.htm
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
PA200 and 8ohm load? CJ900RR Chip Amps 9 7th March 2007 04:44 PM
Exchange JBL2118J (16ohm) for 8ohm or blown drivers (UK) Puggie Swap Meet 0 23rd May 2006 09:05 AM
150 Watt / 8ohm @ 30V or 55V with good efficiency? didifeed Solid State 27 23rd February 2005 07:36 PM
Good & simple chip amp for 2-ohm load? Otherwise Chip Amps 7 8th July 2003 07:21 PM
Halving Power Disssipation ding Solid State 1 15th June 2001 12:54 AM


New To Site? Need Help?

All times are GMT. The time now is 01:52 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2