Dear all,
I have an old tube radio (schema: https://gejoweb.wordpress.com/x-philips-b5x43a-schema/), with singe end EL84 output.
Now I would like to change the original output transformer into Lundahl LL2765, and used it in the line-in mode as a headphone amplifer (https://www.lundahltransformers.com/wp-content/uploads/datasheets/2765.pdf), given the output impedence for EL84 is around 5k.
My questions are:
1. Is it worthy to do so, given the old architecture of the original schema? Or it is a good idea to DIY a new one with the pair of LL2764?
I am also interested to know the possibility of reusing LL2765 for 300B.
2. What is the output impedence for 300B? I checked online, and got answers from 3k to 5k. What is the best performing impedence range for 300B?
3. Would LL2764 be a good fit for 300B?
Thank you.
I have an old tube radio (schema: https://gejoweb.wordpress.com/x-philips-b5x43a-schema/), with singe end EL84 output.
Now I would like to change the original output transformer into Lundahl LL2765, and used it in the line-in mode as a headphone amplifer (https://www.lundahltransformers.com/wp-content/uploads/datasheets/2765.pdf), given the output impedence for EL84 is around 5k.
My questions are:
1. Is it worthy to do so, given the old architecture of the original schema? Or it is a good idea to DIY a new one with the pair of LL2764?
I am also interested to know the possibility of reusing LL2765 for 300B.
2. What is the output impedence for 300B? I checked online, and got answers from 3k to 5k. What is the best performing impedence range for 300B?
3. Would LL2764 be a good fit for 300B?
Thank you.
Last edited:
Radios generally aren't hifi devices. So IMHO it is unncecessary to make any changes. Quality of audio is cut in the RF & FI stages to less than 10KHz usualy, thus max audiofrequency is limited to 5KHz and low side by the coupling capacitors and the supply filtering.
Hi Osvaldo de Banfield,
Thank you for your response. I was not making myself clear, sorry for that. I would like to use it in the line-in mode from mp3, instead of using it to hear radio.
In this case, would it be worthy to do so?
Thank you for your response. I was not making myself clear, sorry for that. I would like to use it in the line-in mode from mp3, instead of using it to hear radio.
In this case, would it be worthy to do so?
Is this radio not working? If it uses a EL 84, why ask about 300B? If the radio does not operate as a radio, strip the good parts for a future project and continue using your computer to listen to MP3's. Why listen to mono mp3? Listen to the original format of the music.
Hi 20to20,
It's working fine. I would like to reuse the LL2765 for 300B.
For the mp3, I meant to use the headphones amplifier in line in mode.
Thanks.
It's working fine. I would like to reuse the LL2765 for 300B.
For the mp3, I meant to use the headphones amplifier in line in mode.
Thanks.
It seems better to me, to keep the radio as it is, and build a new (tube or not) for the mp3 player.
EL84 was designed with high gain to reduce tube count in receivers. So, if you can build a simple EL84 amplifier with a commo trafo and a, say, a good 250VDC power supply, you can enjoy building your mp3 amplifier. It is not too difficult. We can help if you are decided. Don't need to waste too much money to start.
Years ago I helped a guy to make a small tube AM transmitter from thrash and with few knowledge. It was an interesting experience for me.
EL84 was designed with high gain to reduce tube count in receivers. So, if you can build a simple EL84 amplifier with a commo trafo and a, say, a good 250VDC power supply, you can enjoy building your mp3 amplifier. It is not too difficult. We can help if you are decided. Don't need to waste too much money to start.
Years ago I helped a guy to make a small tube AM transmitter from thrash and with few knowledge. It was an interesting experience for me.
Your Pallas radio audio amplifier is not a good candidate for Hi-Fi conversion because Philips fitted it with a design tailored for radio application, and the frequency responce is purposefully not flat. The preamplifier stage does use the grid leak, so global feedback is applied to the lower end of the volume potentiometer. This means that volume cannot be turned to zero and feedback is lowered when the volume is turned up. This does make a lot of sense on AM radio because audio gain is increased and bandwith is lowered when the signal is weak. Output transformers on that radio are very small and have the auxiliary primary tap for hum reducing purposes, this is matched with the AD3800 speaker (70Hz resonance) to attenuate the hum due to insufficient supply filtering and the complex wiring/switching arrangement of the elaborate tone controls typical of the period.
This is the schematic of my headphone amplifier, basically a implementation of the Osvaldo's suggestion. I started the project more than a year ago and I've tested many output transformers and tubes. I currently use the end pentode section of the EFL200 tube in a decal to octal socket adapter instead of the EL34: plenty of gain and very low distortion. EL84 also works well on this circuit. EFL200 is a decal tube, the european response to compactrons. Very good tubes and readily available at low prices, but no one is currently using them due to lack of sockets and popular audio circuits: they have only been briefly used on bw TV sets. EFL200 as low-power audio output tube is a suggestion I've found in a old Ialian magazine from the '60, and it works very well indeed on this role. Due to the frame grid construction I was expecting some microphony, but there is none.I found out that a special headphone output transformer is not needed, a regular 5k to 8 ohm 5W transformer works well for my headphone requirements.
