Transformer - Output, 8 W, Single Ended
Specifications
| Power | 8 W |
|---|---|
| Primary Impedance | 5,000 Ω single-ended |
| Secondary Impedance | 8 Ω |
| Primary DC Resistance (Red to Blue) | 230 Ω |
| Mounting Centers | 2.375" |
| Mounting Type | U-bracket |
| Weight | 0.7 lbs |
Wiring:
SKU:
P-T31
Item ID:
003561
RoHS Compliant
| Item Height | 1.606 in. | |
| Item Length | 2.8 in. | |
| Item Width | 1.9 in. | |
| Mounting Hole Center to Center A | 2.35 in. | |
| Mounting Hole Diameter | 0.187 in. | |
| Mounting Type | U-bracket | |
| Power | 8 W | |
| Primary D.C. Resistance, blue-red | 230 Ω | |
| Primary Impedance | 5 kΩ | |
| Secondary Impedance | 8 Ω |
| Packaging Dimensions | 2.8 in. × 1.6 in. × 1.8 in. | |
| Weight (Packaging) | 0.676 lbs. |
 Wiring | All Models |
My Project Lists
Specifications, Files, and Documents
Questions and Answers
Click each question to see its answers.
3 answers
Hi: I want to built an stereo amplifier Hi-Fi with single ended audio transformers, I was searching the store and the frequency response are only
10Khz like for a guitar amp,any audio transformer with a list 40hz to 20Khz?
Thanks
Alfred
Asked by Anonymous on April 2nd, 2016.
April 5th, 2016
Staff MemberTop Contributor
Most of our current transformer stock will be leaning towards guitar amplification. I would suggest checking out the Hammond offerings as those would have the best chance of meeting your needs.
Look at the offerings from One Electron.
At 8 watts max. (5watts RMS), you won't even notice the loss of bass below 100Hz. Additionally, most people are unaware of frequencies over 5000Hz (Acoustical Engineering, Olson, 1957).
3 answers
WILL THIS TRANSFORMER WORK WITH THE 6V6 AUDIO TUBE?
Asked by Anonymous on June 30th, 2016.
June 30th, 2016
Staff Member
By looking at the spec sheet above, this transformer should work with 6V6, 7C5, and 6AQ5/A tubes.
It worked with my 6V6 output tube guitar amp.
It worked just fine with a 6aq5 tube also.
3 answers
What is the max DC bias for this OT?
Asked by Anonymous on February 22nd, 2017.
February 23rd, 2017
Staff Member
The maximum DC bias depends on the tube being used, the plate voltage, and the value of the cathode resistor.
I think this question was not referring to tube bias, but maximum DC a single-ended transformer was designed for (or is recommended). That is a common spec from transformer manufacturers and should be observed to avoid core saturation. It's much less of a concern for push-pull because it's normally balanced or can be adjusted to be.
Thanks
Let's read between the lines, in case there is no published spec (available) from the manufacturer.
The transformer is recommended for 6V6, 7C5 and 6BQ5. The 7C5 is the Loctal socket version of 6V6, so let's say there are only two tubes we know are suitable. I found one version of Fender Champ schematic that had a cathode voltage of 19 VDC with a 470 ohms cathode resistor. 19/470 = 0.04A = 40 mA.
2nd example I looked up was for a 6BQ5/EL84 SE amp with 7.7 VDC cathode voltage and a 150 ohm cathode resistor. 7.7/150 = 0.051A = 51 mA.
Those may not maximum allowable, but based on the recommended tubes and mostly satisfied users we can assume 51 mA DC is OK.
2 answers
What kind of speaker should I use on the P-T31 transformer. I am restoring an old GE E-61 radio and the speaker and transformer are missing. Hoping this transformer will work, but not sure what kind of 8" speaker I need next.
Asked by Anonymous on April 18th, 2016.
April 19th, 2016
Staff MemberTop Contributor
From what I can see you would want to use an 8 ohm speaker with this transformer.
Hi:
I just finished a full restoration on that same model.The speaker size should be 6 1/2 inches.In order to replace the speaker you should place a 1K 25W resistor as a substitute for the coil that was used to create magnet for the old speaker.The audio output PT-31 will work without any problem
2 answers
Hey will this work with an EL34?
Asked by Anonymous on January 24th, 2021.
January 27th, 2021
Staff Member
Since it is only rated at 8W, this would not be a great choice for an EL34.
In addition to low power handling capabilities, the primary impedance is incorrect.
1 answers
What is the distance between mounting holes?
Asked by Anonymous on April 29th, 2016.
April 29th, 2016
Staff MemberTop Contributor
The distance between mounting holes is 2-3/8".
1 answers
How many pins does a 6V6 and 6J5 tube have?
Asked by Anonymous on June 30th, 2016.
December 16th, 2016
Staff Member
Both a 6V6 and a 6J5 tube have 8 pins each. If you are asking how many used or active pins, the answer is different. A 6V6 is a pentode. A 6J5 is a triode.
1 answers
Will this transformer work with an El84/6BQ5 tube?
Asked by Anonymous on September 13th, 2016.
September 14th, 2016
Staff Member
Yes, this transformer should work with the El84. We use this transformer with our MOD102 Kit: K-MOD102.
1 answers
If this transformer isn't for the EL84, what one do you recommend for a single end?
Asked by Anonymous on October 22nd, 2016.
October 26th, 2016
Staff Member
Hello, this transformer should work with EL84 tubes.
1 answers
Is this transformer current production or surplus stock?
Asked by Anonymous on October 23rd, 2016.
October 26th, 2016
Staff Member
Hi, this is a current production transformer.
1 answers
Where are these made?
Asked by Anonymous on November 20th, 2017.
November 20th, 2017
Staff Member
These are made in Mexico.
1 answers
What is the primary side inductance of this device?
Asked by samlcompton on November 20th, 2018.
November 21st, 2018
Staff Member
3.1 H
1 answers
would this be a good replacement for a zenith 9s367 with 6f6 single end output----thanks
Asked by Anonymous on January 10th, 2020.
Yes this will work with 6F6. They are very identical tubes
1 answers
If I use this with a 4 ohm load, will the primary impedance be too low for a single 6bq5/el84?
Asked by Anonymous on April 16th, 2020.
April 17th, 2020
Staff Member
We would only recommend using this with a matching 8 ohm load.
1 answers
What would be a good power transformer to go with this?
Asked by Anonymous on January 9th, 2021.
January 15th, 2021
Staff Member
The power transformer should be determined using the full circuit since different tubes and choices like the rectifier type will need specific voltages from the power transformer.
1 answers
Will this work with a ecl82 tube?
Asked by Anonymous on September 30th, 2022.
September 30th, 2022
Staff Member
We have no experience using the ECL82 with this transformer so we cannot say for certain if it will work well or not. Looking at the datasheet, it would appear to be compatible.
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Product Reviews
Great replacement for my Antique Radio projects.
Hi
The audio output Xfmr was installed on 1938 old GE radio and it worked perfectly
Perfect match for the amplifier I am building. Good quality and workmanship.
Good price too.
I HAVE NOT TRIED THEM YET. I PURCHASED 2 OF THE XFMRS TO BE ABLE TO CONNECT 8 OHM SPEAKERS TO MY VINTAGE HALLICRAFTER AND COLLINS RADIOS.
Excellent quality great product!
Restoring a 1941 Zenith 7s529 radio. The audio output transformer was “open.” Took a chance and bought the PT 31 transformer. Installed the new transformer and the radio came back to life!! The mounting holes do not line up. Made up my own bracket and good to go! Highly recommend this transformer!!
I have used a bunch of these transformers in a number of single ended audio amplifiers using a variety of final output tubes including the 6F6, 6V6, 6L6 and 12BH7. Projects include a 1939 vintage regenerative receiver, single ended stereo amplifiers and a stereo headphone amp. Testing with a signal generator and an oscilloscope yields a flat response from about 100 Hz up to 20kHz. The roll off is gradual down to about 20Hz. Since my speakers [big Pioneer CS-V9910's] roll off at about 40Hz, these are are ideal , especially for the price. As long as I keep building low-power audio amplifiers, I'll keep using these.
I was rebuilding a small antique guitar amp from the early ‘50s, and found that they had substituted the case and thus the speaker, and thus the output xformer (because it was mounted to the speaker in this amp). I wondered if a different transformer would make a difference in the sound output level. The power tube is a single ended 6V6. Others indicated that this transformer should work for a 6V6, so I ordered it. I’m happy to say it works very well with my 6V6 circuit, with no modifications necessary. This xformer had a different primary winding resistance than the one that has been substituted. Since it did boost the output volume a bit, I think the 6v6 output tube had been trying to feed a mismatched transformer.
Since repairing old tube radios is just a wintertime hobby, I do not like to get much invested in it. I found this transformer to be a cost effective replacement for most of the 30s and early 40s radios. Performance is great.
This output transformer worked fine on a Majestic 1770 with a single 6K6 output tube.