Re: {Collins} 6BF5 vs. 6AQ5 in 75S-3, B, C



Dick

Thanks for your input.

Since the test setup was still in place it was easy to make the bias change and run the measurements again. I tried several values of resistors and 390k worked best for 'centering' the waveform so that onset of clipping was equalized top and bottom of the waveform. Test results are a follows:

Gain: 6AQ5 gain -5 dB referenced to 6BF5

Frequency response: same

THD:

.125 W   3.6%

.25 W   4.5%

.5 W  8.0%

.75 W  15.6%

Maximum output power only slightly higher

It's apparent that the bias change is worthwhile in reducing THD when using a 6AQ5. If it's okay with you I'll add this information to the webpage giving you credit for the modification.

Jay W1VD


----- Original Message ----- From: "Dick Weber" <dwebtx@xxxxxxxxx>
To: "collins" <collins@xxxxxxxxxxxxx>
Sent: Thursday, March 13, 2014 4:54 PM
Subject: Re: {Collins} 6BF5 vs. 6AQ5 in 75S-3, B, C


Gentlemen:

There is other information about "6BF5 vs. 6AQ5" that may be helpful that is in the reflector's archives. Do a search on K5IU and you will find 5 posts on the subject. None of these have THD information, but do cover power consumption tests results including tests for a 6AQ5 with and without the bias changed.

I'd sure like to see the THD/output power tests done with the 6AQ5 where the bias has been set to the -6 to -7 vdc range. This is easily done by tacking in a 330-390k, 1/8 Watt resistor from V10, pin 1 to ground. After testing, the resistor can be easily removed or left in if you plan to use a 6AQ5... or not...

Regards,
Dick, K5IU





________________________________
Dennis Monticelli <dennis.monticelli@xxxxxxxxx>
To: jrusgrove@xxxxxxxxxxx
Cc: collins <collins@xxxxxxxxxxxxx>
Sent: Thursday, March 13, 2014 2:43 PM
Subject: Re: {Collins} 6BF5 vs. 6AQ5 in 75S-3, B, C


Excellent report, Jay. Thank you. A good addition to our body of
knowledge on the S-line.

Fortunately, audiophiles don't give a hoot about the 6BF5.

Dennis AE6C


On Thu, Mar 13, 2014 at 12:27 PM, <jrusgrove@xxxxxxxxxxx> wrote:

Finally found time to make a few measurements last night ... results at:

http://www.w1vd.com/6BF56AQ5.html

Jay W1VD
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