Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on June 12, 2015, 08:39:19 am

Title: OT question
Post by: dude on June 12, 2015, 08:39:19 am

I have an old single-ended OT, 10K5 @ 8 0hms and 5.2K @ 4 ohms.  Seems a little high for a 6V6.

Which would I get the most volume from, the 6V6 @ 8 ohms (would like to see around 8K) or 6L6 @ 4 ohms (like to see around 5K)? So, seems the OT would be better suited for a 6L6...?

But I want to use a 6V6, should I run it with a 4 or 8 ohm spk.

Thanks,
al
 

Title: Re: OT question
Post by: shooter on June 12, 2015, 10:21:48 am

kinda sorta depends on your B+, the tube chart shows 5k at 250vdc but 8.5k at 315vdc.

Title: Re: OT question
Post by: kagliostro on June 12, 2015, 10:26:00 am

Shooter you preceded me, you are the fastest shooter of the forum  :icon_biggrin:   :thumbsup: :thumbsup: :thumbsup:

(http://cdn-static.denofgeek.com/sites/denofgeek/files/tombstone.jpg)

+ 1 for Shooter I was about to say the same thing

give a look to the datasheet

http://www.mif.pg.gda.pl/homepages/frank/sheets/121/6/6V6.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/121/6/6V6.pdf)


(http://i.imgur.com/8zwBWQ9.jpg)

K

Title: Re: OT question
Post by: shooter on June 12, 2015, 12:22:34 pm

Quote

fastest shooter

I got the name from an 'ol guy, I was wearing a '40s trench coat one day and he yelled out "hey shooter"
and it stuck!  my actual shooting skills are not that good, 3 outta 5 on a paper plate from my 30-30 at 80yrds, open sights.

Title: Re: OT question
Post by: kagliostro on June 12, 2015, 01:41:26 pm

it is a long long time I didn't shoot

I was fond of standard 22LR rifle shooting at 50 meters


(http://www.tsnadria.it/files/carabina-walther-cal-22-monocolpo-800-x-600.jpg)

but that was in one other life  :icon_biggrin:

Franco

Title: Re: OT question
Post by: dude on June 12, 2015, 10:05:05 pm

You guys are crazy, Doc Holiday.... :laugh:

Yeah, I saw that chart but who runs B+ voltage less than 325v yet 250v.

Running 380v B+, cathode biased.

I really can't tell the difference in sound levels between 4 or 8 ohms with the 6V6, just wondering if the PT is getting stressed as the single 6V6 wants around 8K, I believe. So it's either 5K5 or 10K5, my guess is use the 8 ohm speaker...?

Title: Re: OT question
Post by: kagliostro on June 13, 2015, 01:12:43 am

About that choice (10.5k with an 8ohm speaker) you are near the best Zout (you miss only near 1.5k of Zout)

I hope my math is correct

Zout = Va/(Pa/Va)

(where Zout the requested output impedance - Va is Volt at Plate - Pa is the dissipation ammissed for the plate of the tube)

so we have

Zout = 380v/(12W/380v)

12/380 = 0.0315789

380/0.0315789 = 12033.351

Zout = 12033.351ohm

not very far from your 10.5k

---

You must set a cathode resistor as to have the tube idle near maximum and use a 470R 2-3W resistor watching to the grid dissipation or you can set it at 50-60v below the plate voltage

---

I hope someone can confirm my math

Franco

Title: Re: OT question
Post by: VMS on June 14, 2015, 05:22:45 pm

Quote from: kagliostro on June 13, 2015, 01:12:43 am

You must set a cathode resistor as to have the tube idle near maximum

I think PRR posted this type of a formula for the cathode resistor value:

Load impedance divided by tube mu times 0,6

10500 / 10 * 0.6 = 630 Ohm