304TL based Class A
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
 1st February 2007, 04:56 PM #11 angelfj   diyAudio Member     Join Date: Sep 2004 Location: Philadelphia First, please accept my apology for this long post and to those (I know you are out there, who see all of this as very elementary) please be patient with me. I am trying to establish the operating point as suggested in previous posts. However, if I go to the tube characteristics for the 304TL, as published by Eimac, they are not the same as the typical representation for a triode. I found an excellent reference on the Internet, and this guy did a wonderful job of explaining, step by step, how to establish the operating point. see: http://www.valveheart.com/ In order to follow the example, I seem to be missing some critical information, for the 304TL, which would normally be included in the characteristics for other tubes/manufacturers. 1. Rp = plate resistance It was suggested that for triodes , the load resistance, Rl, also referred to as the output transformer primary impedance, can be calculated as 2 - 6 x's Rp. So, if I do not know what is the Rp, I can not calculate Rs, which is critical for calculation or a graphical check for the operating point. 2. The example uses a graphical representation of the tube operation. The horizontal axis represents plate voltage, and the vertical axis represents plate curent. Superimposed on this graph are curves for several values of grid bias. The Eimac data is very different. There are two types of curves. The first is a graph of power output (watts) horizontal axis VS grid driving power (watts)) vertical axis , for a fixed value of plate voltage (Eb). Each of these graphs show several curves for different values of Ec (cathode voltage???). The second type of graph, and there is only one, has plate voltage on the horizontal axis and grid volts on the vertical axis. Several curves are drawn for both different levels of plate current and grid current. So, it seems that these graphs are not suitable for the graphical determination of the operating point. Can someone offer a little help? I have to believe that establishing the operating point fpr a 304TL, to be used in a SE, class A amp has been done before. In the spirit of not re-inventing the wheel, please induldge by curiosity. My only limitations are the voltage and capacity of my plate transformer, which will be limited to approx. 2000 vdc @ 500 ma. Thanks in advance, Frank
 2nd February 2007, 03:38 AM #12 angelfj   diyAudio Member     Join Date: Sep 2004 Location: Philadelphia To all: Two questions regarding tube filament requirements: 1. which is better ac or dc? 2. how critical is the voltage? For example the 304TL requires 10 volts @12.5 amps. I have located a transformer rated 12 volts @ 25 amps. \$30 each , not center-tapped. Would 2 more volts kill the filaments? I was thinking of taking the transformers apart and removing turns, until I got 10 volts with a load to simulate the tube filaments. Or putting a variac in the primary. What do you think? What about not having a center tap. Is this a game stopper? Thanks, Frank
 2nd February 2007, 03:58 AM #13 wfmali   diyAudio Member   Join Date: May 2003 Hello, I would tentativly go DC, in order to avoid hum - and you have to use the right filament voltage - I would not even try 20% overvoltage short term. If I would have to light this beast, I would go SMPS right away. You could use a standard 9V supply and adjust to max. voltage. The only problem could be that hiccup supplies might not start on cold filaments, current limiting would be better. Or, use a 12V supply, adjust to min. voltage and drop some .5V or so in a resistor. That will work with hiccup overcurrent protection as well. Marcus
 2nd February 2007, 12:27 PM #14 nhuwar   diyAudio Member     Join Date: Jan 2007 Location: Cypress Texas On most eimac tubes the filament voltage at beam on state is not to vary more then 5% also you should not apply full filament voltage at turn on. There are maximum current limits on the filament and they can only be exceeded applying full voltage to a cold filament. There is also a minimum heating time before plate voltage can be applied usually 3 to 5 minuates for transmitter tube. Nick
 3rd February 2007, 12:04 AM #15 Dave Cigna   diyAudio Member     Join Date: Oct 2003 Location: Finger Lakes, NY I don't think you'll be happy with AC because of the very high mu. Also, the 304TL is essentially four 75TL's in one bottle, all connected in parallel. Well, not everything is always in parallel. The 10V@12.5A connection puts one pair of filaments in series with the other pair. The consequence is that with DC two of the sections will be running with 5V more/less bias than the other two. Using the 5V@25A connection puts all of the filaments in parallel so that all four sections bias up the same. -- Dave
 3rd February 2007, 01:19 AM #16 rdf   diyAudio Member     Join Date: Jun 2004 Location: big smoke I didn't realize that about the 304TL filaments. The obvious question: is it possible to feed each section with an independent winding in opposite phase to reduce hum?
 3rd February 2007, 05:12 AM #17 Gluca   diyAudio Member     Join Date: Nov 2004 Location: Back to Italy huuuumm 304TL has 2 filaments to be connected in parallel @ 5V (or series @ 10V) ... if you connect two 5VAC secondary windings 180deg out of phase you get 0V, don't you? Ciao Gianluca
 3rd February 2007, 06:24 AM #18 rdf   diyAudio Member     Join Date: Jun 2004 Location: big smoke The data sheet shows two isolated, completely independent filaments. I was thinking along the lines of a centre-tapped 5 volt transformer to each filament, each filament transformer's centre tap tied to ground.
 3rd February 2007, 08:21 AM #19 Gluca   diyAudio Member     Join Date: Nov 2004 Location: Back to Italy mmmm ... that makes sense to me. Anyone out there is running 304TLs and would care to give it a try?? Gianluca
 3rd February 2007, 12:22 PM #20 angelfj   diyAudio Member     Join Date: Sep 2004 Location: Philadelphia It seems that most people are recommending DC filament supply only for SE. 304TL in class A. The reason they say is that ac filament supplies introduce too much noise. I am certainly no expert, but this seems logical. Regarding independent filaments, I believe that these 5-volt filaments are electrically isolated. I had plan to connect them in series and us a 10 volt DC supply. This will be based on a salvaged welding transformer that can easily deliver 30 -40 amps at 12 volts. However, I don't believe that the tube cares how the cathode is heated.

 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 Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post nhuwar Tubes / Valves 27 4th September 2010 12:50 AM aramosfet Class D 3 12th April 2009 07:37 AM Brisso57 Solid State 4 14th February 2007 10:30 AM ukram Digital Source 21 19th January 2004 11:38 AM

 New To Site? Need Help?

All times are GMT. The time now is 05:49 AM.