Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on January 22, 2018, 02:46:22 am

Title: 6U8 vs 6U8A - is the difference only in heather Warm-Up time ?
Post by: kagliostro on January 22, 2018, 02:46:22 am

Is the difference between 6u8 and 6U8A only in heather warmup time ?

http://frank.yueksel.org/sheets/168/6/6678.pdf (http://frank.yueksel.org/sheets/168/6/6678.pdf)

https://frank.pocnet.net/sheets/049/6/6U8A.pdf (https://frank.pocnet.net/sheets/049/6/6U8A.pdf)

Thanks

Franco

Title: Re: 6U8 vs 6U8A - is the difference only in heather Warm-Up time ?
Post by: VMS on January 22, 2018, 05:10:07 am

According to this page the answer is yes:


http://www.r-type.org/exhib/aaa1389.htm (http://www.r-type.org/exhib/aaa1389.htm)


http://www.r-type.org/pdfs/6u8.pdf (http://www.r-type.org/pdfs/6u8.pdf)


http://www.r-type.org/pdfs/6u8a.pdf (http://www.r-type.org/pdfs/6u8a.pdf)

Title: Re: 6U8 vs 6U8A - is the difference only in heather Warm-Up time ?
Post by: kagliostro on January 22, 2018, 02:34:18 pm

Thanks VMS

Franco

Title: Re: 6U8 vs 6U8A - is the difference only in heather Warm-Up time ?
Post by: PRR on January 23, 2018, 03:37:40 pm

They may be the same.

In series-string heaters it is best if all the heaters warm-up at the same rate. A standard rate was picked, and some (not all) the "A" tubes meet that spec. However the spec was picked to be similar to how most existing tubes warmed-up. I suspect only a few extreme types, or odd makers, actually had to  change their heater designs.

Huh. The magazine Popular Science ran a very fictional story/article about the change. Because it is a boring subject, the author jazzed it up with a horse-betting story and Runyon-esque slang. This may not read well if you are not an older American, but you will get the idea. "11 seconds" is a simplification; I inserted the actual spec.

Title: Re: 6U8 vs 6U8A - is the difference only in heather Warm-Up time ?
Post by: kagliostro on January 23, 2018, 05:11:10 pm

Thanks PRR

I like very much your explanation (and saved the article in my archive)

Franco