Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on March 26, 2024, 01:25:30 pm

Title: 8417 Power Tubes
Post by: plexi50 on March 26, 2024, 01:25:30 pm: I have a stash of NOS ECG Phillips 8417 Power Tubes. Any info for what these might be used in today?
I read they are a sub for 6550/KT88 tubes. Is that correct? I have them listed on FB Market Place.
Title: Re: 8417 Power Tubes
Post by: DummyLoad on March 26, 2024, 03:25:08 pm: Quote
I read they are a sub for 6550/KT88 tubes.

Not exactly, more like a 6L6GC on steroids. They have an achilles heel inherent in the design, since they have such a high slope with very low drive requirements, this requires that the elements be much closer together than any other power pentode ever made for audio, that issue can cause internal shorts in equipment that are subject to excess vibration such as bass amps and combo amps. IMO, they are best left for use in HiFi gear if originally equipped. Flip them if have no use for them. On the same subject, it seems some actually sub 6L6GC or 6550/KT88 and mod the driver circuit(s) to accommodate lower drive sensitivity.

--Pete
Title: Re: 8417 Power Tubes
Post by: plexi50 on March 26, 2024, 04:46:26 pm: Yes i read where they were suited for Hi-Fi gear. Better left in that area.
Title: Re: 8417 Power Tubes
Post by: HotBluePlates on March 26, 2024, 07:47:26 pm: Quote from: plexi50 on March 26, 2024, 01:25:30 pm
... 8417 Power Tubes. Any info for what these might be used in today? ...

They are useful for the Sano amplifier owners who haven't converted their amps to use EL34.

I have one such beast, and just haven't gotten around to checking the circuit doesn't need help using the EL34. Just looking at the innards of the 8417, you can see the screen grid is WAAYYY close to other internal elements (which is how they might self-destruct).
Title: Re: 8417 Power Tubes
Post by: plexi50 on March 27, 2024, 07:14:35 am: I will take a peek today and look at the elements.
Title: Re: 8417 Power Tubes
Post by: PRR on March 27, 2024, 09:01:54 pm: If you have to ask: just sell them. They are worth MUCH more to someone who needs them, in circuits designed for them.
Title: Re: 8417 Power Tubes
Post by: plexi50 on March 28, 2024, 06:32:12 pm: Not to many changes! Interesting tube to me.
Title: Re: 8417 Power Tubes
Post by: HotBluePlates on March 29, 2024, 06:20:52 pm: Quote from: plexi50 on March 28, 2024, 06:32:12 pm
... Interesting tube to me.

"Scary tubę" to me. It's just itching to have G2 short-circuit to G1 & burn down stuff.
Title: Re: 8417 Power Tubes
Post by: plexi50 on March 30, 2024, 09:49:11 am: It's a shame that the elements are so close together. Good looking glass though.
Title: Re: 8417 Power Tubes
Post by: shooter on March 30, 2024, 10:45:56 am: Quote
Good looking glass though.
one more Plus for the HiFi folk, looking good pays better