trinityamps.com

Looks familiar very nice!

I used a pic found on this forum as model for Stephen (exactly the kind of black Tolex/grillcloth I wanted), it was yours ?!

Wiring finally done !!!



Some details :



Now, I need to check all wiring before powering up for testings.
Speaker installed in cab, ready for testing :

Nice and neat build. I'm sure it will be great!

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Normally we have stock of cabinets but we ran put due to demand. Also, this was a 112 not the typical 110.
We are back up in stock of bare cabinets again.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

>> I used a pic found on this forum as model for Stephen (exactly the kind of black Tolex/grillcloth I wanted), it was yours ?!

Yeah, probably. I think Stephen's reaction was "You really mean ALL BLACK?"

Killer amp, my favorite...nice build, btw!

Thanks mmarsh!


Tested voltages then tried with a guitar, and the amp worked great.
Here are voltage measurements:

Without tubes :
HV before rectifiers : 660VAC
HV after rectifiers : 456 VDC

With tubes :
VRM Position Idle : 94 VDC
VRM Position 4 : 107 VDC
VRM Position 5 : 119 VDC
VRM Position 6 : 132 VDC
VRM Position 7 : 146 VDC
VRM Position 8 : 183 VDC
VRM Position 9 : 273 VDC
VRM Position 10 : 405 VDC
VRM Position Max : 418 VDC


Measurements with 402 VDC after VRM (C12) :

After R10 : Expected 340 VDC, Measured 333 VDC, Variation 2.1%

Mode Tweed Cathode resistor : 732 ohms
12AX7 Plate 1 (pin 1): Expected 203 VDC, Measured 182 VDC, Variation 10.3%
12AX7 Cathode 1 (pin 3): Expected 1.70 VDC, Measured 1.79 VDC, Variation 5.3%
12AX7 Plate 2 (pin 6): Expected 191 VDC, Measured 186 VDC, Variation 2.6%
12AX7 Cathode 2 (pin 8 ): Expected 1.70 VDC, Measured 1.61 VDC, Variation 5.3%
Mode 'tude
12AX7 Plate 1 (pin 1): Expected 199 VDC, Measured 179 VDC, Variation 10.0%
12AX7 Plate 2 (pin 6): Expected 152 VDC, Measured 145 VDC, Variation 4.6%
Current Rp1 = (333-182V)/218.3Kohms = 151/218300 = 0.69 mA
Current Rp2 = (333-186V)/213.3Kohms = 147/213300 = 0.69 mA
Current Rk1 = 1.79V/2.659Kohms = 1.79/2659 = 0.67 mA
Current Rk2 = 1.61V/2.657Kohms = 1.61/2657 = 0.61 mA

6V6 Plate (pin 3): Expected 399 VDC, Measured 400 VDC, Variation 0.25%
6V6 Screen (pin 4): Measured 396 VDC
6V6 Cathode (pin 8 ): Expected 29 VDC, Measured 25.2 VDC, Variation 13.1%
Current Rk = 25.2V/739ohms = 0.0341 A = 34.1 mA

Heaters: Expected 6.3 VAC, Measured 6.98 VAC, Variation 10.8%


All voltages are acceptables, within 15% of expected voltages. Plate voltages on 12AX7 are a bit low, and 6V6 is a bit underbiased, but the amps works fine. There is a volume step with the VRM past 8, and this is expected according to the voltages readings.

The only thing that bothers me is the heater voltage, 6.98VAC is high, but many others builders are getting the same 6.98-7.0VAC. Stephen, would you do the diodes trick http://www.trinityamps.com/phpbb/viewtopic.php?f=12&t=3598 withi this voltage ? My fear is that it will shorten the life of tubes...

Some pics :




Top with Mojotone's oxblood chikenheads knobs :


The amp with its new best friend, my SG :

I have checked the heaters voltage again after some days, and the voltage is even higher, measured 7.05 VAC (late in the evening, I suppose that the line voltage is a bit higher when the load is reduced). So I have done the diode trick.

Here is the heater current for possible tubes:
12AX7 = 0.3A @6.3V
6V6 = 0.45A @6.3V
6L6 = 0.9A @6.3V
EL34 = 1.5A @6.3V
KT66 = 1.3A @6.3V
KT88 = 1.6A @6.3V

So to use a EL34 or KT88 (plus the 12AX7) the current draw will be 1.9A, the diodes need to be rated at over 4A. I used On Semiconductor MUR860 in TO220 package (8A current rating) as I have some lying around.

Here are the diodes assembly (with the remaining of the heater wire provided with the kit) :



And once installed in the amp :



Measurements after adding the diodes
Heaters: Measured 6.82 VAC without tubes
Heaters: Measured 6.20 VAC with tubes

That's perfect, it will save my precious NOS tubes; it didn't matters if the voltage is between 6.0 and 6.3V, the tube works well even with a slightly reduced emission.