Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on September 08, 2025, 03:51:52 am

Title: How to identify a tube in the ecl/pcl range ???
Post by: kagliostro on September 08, 2025, 03:51:52 am

Yesterday I've find in my stock about 10 tubes I got 7 years ago

they are surely NOS, selled without a box (if I remember correctly I payed it really on the cheap)

They are surely triode/pentode tubes but on it there isn't a standard Tube Label, only a number

My memory is I got it as ecl8* or pcl8* tubes but I don't remember if they are the 82 or 84 or 86 models, may be pcl86 but not sure at all  :BangHead: :BangHead: :BangHead:


What can I do to identify it correctly ? (I've an emission tube tester to perform measures, the other one that can measure gm need some manutention)

Many Thanks

Franco

Title: Re: How to identify a tube in the ecl/pcl range ???
Post by: Merlin on September 09, 2025, 08:47:04 am

The 86 looks very different from the other two, so you could start by looking at photos. The 82 and 84 have totally different pinouts, so should be easy to identify. What number is on them?
You can figure out P or E by applying 6.3V and measuring the heater current.

Title: Re: How to identify a tube in the ecl/pcl range ???
Post by: kagliostro on September 09, 2025, 02:21:21 pm

Molte Grazie Merlino

I had some problem to solve and no time to perform test, however looking to the tube it seems to be of the 86 class, not 82 or 84

I was thinking ... can I measure the resistance of an ecl86 heater and compare it with the resistance of the heaters of the unknown tube ?

Here attached photo of a pair of the unknown tubes and of an ecl86 tube, the one on the right is an ecl86

Unfortunately the number on the unknown tubes vanished and only two has on it something of readable but not in good shape however

the number seems to be 7 4 2 1 but about the last number I'm not sure it's a 1

Thanks

Franco

Title: Re: How to identify a tube in the ecl/pcl range ???
Post by: Merlin on September 10, 2025, 03:38:04 am

Quote from: kagliostro on September 09, 2025, 02:21:21 pm

can I measure the resistance of an ecl86 heater and compare it with the resistance of the heaters of the unknown tube ?

Cold heater resistance can vary a lot, I would not trust it. I would measure the actual heater current.

Title: Re: How to identify a tube in the ecl/pcl range ???
Post by: kagliostro on September 10, 2025, 06:13:05 am

Thanks Merlin

Yes that Is true

but anyway a 6.3v heater resistance will be lower than a 13.3v heater and this will happen with warm heaters and cold heaters

I did a bit of math using the voltage and the current of each tube (ECL86 and PCL86) to find the warm resistance of each tube, then a search on the web and I find that the cold resistance will be in the order of 1/6 - 1/8 of the warm resistance

I measured the resistance of a cold ECL86 heater and it is 2.4ohm, the unknown tubes cold heaters measured 8.4ohm, this Is within what was espected and I think I can identify the unknown tube as to be PCL86

Franco