Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chasingpeacde on January 15, 2011, 11:27:03 pm

Title: How do I tell if my EH6L6GC power tubes are matched?
Post by: chasingpeacde on January 15, 2011, 11:27:03 pm: I tried the search function here without any luck. Is there some kind of marking on the tubes themselves or the boxes that they came in? Thanks.
Title: Re: How do I tell if my EH6L6GC power tubes are matched?
Post by: Pleximan on January 16, 2011, 12:00:22 am: For current draw it should be apparent when you bias the amp or check the bias.

Some tube suppliers write matching info on the box and some put a sticker/label on the tube base.
Title: Re: How do I tell if my EH6L6GC power tubes are matched?
Post by: jeff on January 16, 2011, 09:34:49 am: Is there more to matching power tubes than current draw at a specific voltage with a specific bias?
Title: Re: How do I tell if my EH6L6GC power tubes are matched?
Post by: FYL on January 16, 2011, 11:36:53 am: Yes. Tubes should be matched for gain - transconductance (Gm) - and current thru the whole working range. Most tubes are only matched for current at 250V or so, some for current and gain, very few are fully tested.

Anyway, this isn't a problem in MI amps: the usual ±5% is fine, even ±10% or more can be OK, as unbalanced tubes can bring some nice disto!
Title: Re: How do I tell if my EH6L6GC power tubes are matched?
Post by: chasingpeacde on January 17, 2011, 11:56:27 am: Thanks for the responses guys! I ordered the tubes from Hoffman here and he sent me the tubes well-wrapped individually but he also sent me the boxes that they came in and they were folded flat. That's why I was thinking that the info on the stickers on the boxes have some relevance regarding that the tubes are matched. Everything on the 4 boxes is identical EXCEPT for these long numbers at the bottom of the stickers. All 4 of the numbers start with "7DAC1009" but they end with "201700D4", "103200C7", "232600C6", and "282C00B9". Do you guys know what that means? Thanks again for all of your help.
Title: Re: How do I tell if my EH6L6GC power tubes are matched?
Post by: FYL on January 17, 2011, 12:10:02 pm: Doug gets so-called "Platinum" tubes from EH, burnt-in or 24 hours and matched in quartets. The numebrs are probably model then batch.