Help me understand tube chart data

brucetassin · 7th October 2011, 03:03 PM

I need a little help. I have an amp with 11BM8 output tubes. I want to upgrade the output transformers (impedance not stated on the schematic) so I looked up the tube chart. From the chart I see "load resistance" as 5.6 k ohms. So I'm assuming the OPT's need to be that or just a little higher. Is that correct?
This is from the tube chart.

Pentode Class A AmplifierPlate Voltage .. 200 V
Grid No. 2 Voltage ............................. 200 V
Grid No. 1 Voltage ............................. -16 V
Peak Grid No. 1 Voltage........................ 6.6 V
Amplification Factor ............................ 9.5
Plate Resistance (approx) ..................... 20K Transconductance .............................. 6400 µ
Plate Current ................................. 35 mA
Grid No. 2 Current ............................ 7 mA
Load Resistance ............................... 5.6K Ω
Power Output (approx) ......................... 3.5 W
Total Harmonic Distortion ..................... 10 %

EddieRich · 7th October 2011, 08:40 PM

The numbers from the datasheet are usually "design guides". The load resistance is probably just the load the manufacturer used to obtain the other numbers. Also, it says load resistance, not impedance, so it was probably a resistor that was used to measure all the other parameters.

If your going to replace the OT's anyways, can you just remove one and measure the impedance? There are several posts on this forum describing ways to measure a transformers impedance, once you have it out of the circuit.

DF96 · 7th October 2011, 08:47 PM

For a small signal valve, the load resistance will be an anode resistor. For an output valve it will be the load presented by the output transformer. It will normally have been chosen to provide a good compromise between maximum output and minimum distortion.

A particular amp may have departed from the data sheet conditions, but probably not by much. Remember that a transformer does not have an impedance, but transforms impedance.

artosalo · 08:55 PM

Yes, 5,6 kilo ohms is correct load impedance for SE output stage when the supply (anode) voltage is 200 V. You can find more detailed data by searching Philips ECL82 (or PCL82).
Correct output transformer is some 5...6 k to 8 ohms ( or 4 ).

7th October 2011, 03:03 PM	#1
brucetassin diyAudio Member Join Date: Dec 2005 Location: Loganville, GA	Help me understand tube chart data I need a little help. I have an amp with 11BM8 output tubes. I want to upgrade the output transformers (impedance not stated on the schematic) so I looked up the tube chart. From the chart I see "load resistance" as 5.6 k ohms. So I'm assuming the OPT's need to be that or just a little higher. Is that correct? This is from the tube chart. Pentode Class A AmplifierPlate Voltage .. 200 V Grid No. 2 Voltage ............................. 200 V Grid No. 1 Voltage ............................. -16 V Peak Grid No. 1 Voltage........................ 6.6 V Amplification Factor ............................ 9.5 Plate Resistance (approx) ..................... 20K Transconductance .............................. 6400 µ Plate Current ................................. 35 mA Grid No. 2 Current ............................ 7 mA Load Resistance ............................... 5.6K Ω Power Output (approx) ......................... 3.5 W Total Harmonic Distortion ..................... 10 %

7th October 2011, 08:52 PM	#4
artosalo diyAudio Member Join Date: Feb 2010	Yes, 5,6 kilo ohms is correct load impedance for SE output stage when the supply (anode) voltage is 200 V. You can find more detailed data by searching Philips ECL82 (or PCL82). Correct output transformer is some 5...6 k to 8 ohms ( or 4 ). Last edited by artosalo; 7th October 2011 at 08:55 PM.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Tube Tester Data	Trout	Tubes / Valves	16	12th May 2011 08:14 PM
Help! can't find ef86 on my Hickok 539b roll chart! and need a tube project	famousmockingbird	Tubes / Valves	4	18th February 2011 12:42 AM
NRI 70 tube chart	lightguy	Tubes / Valves	1	18th November 2007 12:15 PM
Tungsram tube data	Diy martin	Tubes / Valves	3	30th December 2004 10:59 AM
online tube equivalent chart	Bas	Tubes / Valves	3	18th January 2003 08:52 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

7th October 2011, 08:40 PM	#2
EddieRich diyAudio Member Join Date: Jun 2011 Location: North of Boston	The numbers from the datasheet are usually "design guides". The load resistance is probably just the load the manufacturer used to obtain the other numbers. Also, it says load resistance, not impedance, so it was probably a resistor that was used to measure all the other parameters. If your going to replace the OT's anyways, can you just remove one and measure the impedance? There are several posts on this forum describing ways to measure a transformers impedance, once you have it out of the circuit.

7th October 2011, 08:47 PM	#3
DF96 diyAudio Member Join Date: May 2007	For a small signal valve, the load resistance will be an anode resistor. For an output valve it will be the load presented by the output transformer. It will normally have been chosen to provide a good compromise between maximum output and minimum distortion. A particular amp may have departed from the data sheet conditions, but probably not by much. Remember that a transformer does not have an impedance, but transforms impedance.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)