Telefunken RV218 power triode

[Tubologic]

I just found a set of three very old TELEFUNKEN RV218(V) triodes, N.O.S and still boxed ! These are big pre-war direct heated power triodes with a max.plate dissipation of 24 W and 440 V max. plate voltage. Low µ (7) and 3.5 K plate resistance , 2.000 µmhos transconductance.
Does anybody here have any experience with this tube, and how does it compare with other DH triodes in the same power range (50, PX25 , 300B , etc..) in a S.E amp configuration ? I'm still hesitating building a S.E amp with these or selling them to some antique-tube collectors. They look very nice but I only have 3 pieces and they will be nearly impossible to replace in the future. Any thoughts ?

[kevinkr]

I would think the fairly high rp would be a concern for designing suitable OPTs.

[JLH]

They sound like a cross between a globe 50 and a 10Y. They have the seductive smoothness of the 50, but the detail of the 10Y. One of the better DHT out there. I heard these in a Larry Moore 10 Squared amp where they were used as the output tube. We listened to VT-52, 50, 801A, 10, 10Y and the RV-218. The RV-218 beat them all hands down. Output transformer was 5K Tango unit wired to reflect 10K to the tubes. I think the operation point was around 425V at 25mA-30mA.

[Tubologic]

Originally Posted by JLH

They sound like a cross between a globe 50 and a 10Y. They have the seductive smoothness of the 50, but the detail of the 10Y. One of the better DHT out there. I heard these in a Larry Moore 10 Squared amp where they were used as the output tube. We listened to VT-52, 50, 801A, 10, 10Y and the RV-218. The RV-218 beat them all hands down. Output transformer was 5K Tango unit wired to reflect 10K to the tubes. I think the operation point was around 425V at 25mA-30mA.

Thank you for your listening impressions and encouraging comments: if only slightly better than a 50 or 10Y , the RV218 would be already a great tube... looks it's even much better. Could you recommend any currently available output transformer ?

[Vinylsavor]

Hi!

The Lundahl LL2735B/30mA would be perfect for these...

You can contact me via PN if you are interested in these. I have some pairs left over

Thomas

[JLH]

Any high quality transformer in the 7K to 10K range that is rated for 25mA to 40mA of current. While the LL2735B looks like it would work well with the RV-218's plate impedance, I'm afraid that it would make it sound too dark. The RV-218 starts to sound a little too dark if you start to go over 10K. I would not recommend a load over 10K, maybe 12K at the very most. The RV-218 sounds more lively with a 5K load, but loses some bass control. The 7K to 10K range seems to be the sweet spot for this tube.

[Vinylsavor]

Hi!

I don't see how a certain value of the load impedance should make a tube sound dark. The transformer alone does not provide any load impedance at all. Only in conjunction with a connected speaker you get your impedance. Now your speaker impedance can be anywhere, even if the speaker manufacturer states a nominal impedance of say 8 Ohm, the actual impedance can deviate largely from that and with it the load the tube sees.

At 7k the amp will provede a very low dampling factor of 2 Which means any impedance variations in the speaker will color the sound. With such a damping factor the speaker impedance should be linearized. If it comes to coloration I'd suspect it is the relation between amp output impedance to the impedance variation of the speaker.

Best regards

Thomas

[JLH]

I believe what I heard was related to a lower damping factor made for less speaker control and a more lively reproduction of the music. With relatively higher reflected impedance, more speaker control took on a more controlled and darker sound.

[Vinylsavor]

Hi!

Yes, that could be the case. In my experience, different speakers react differently to damping factor. So with other speakers the higher impedance (higher winding ratio) might sound better

Thomas