First time #183 Build

[Structo]

Long plate 12ax7's can be problematic in some gain stages with microphonic noise or filament rattle.

However, long plates can be used in most phase inverters and work great.

If you just buy a few vintage tubes a month and have a nice collection before too long.

[MusicMaker]

Been looking into building a cabinet, but found this on ebay

V-Boutique USA Unloaded D-Style 1 x 12 Unloaded Cab

$249 + $35 shipping. It's made w 3/4" birch. Not sure I could make it cheaper or as good.

A good deal?

[jam-mill]

Been looking into building a cabinet, but found this on ebay

V-Boutique USA Unloaded D-Style 1 x 12 Unloaded Cab

$249 + $35 shipping. It's made w 3/4" birch. Not sure I could make it cheaper or as good.

A good deal?

I own on of these (http://stagecraftgear.com/product/elite-1x12/) ; only $10 more, shipping price is same.

[tubelectron]

Congrtulations MusicMaker : this gives me ideas for my 1st Dumble-like amp project to come...

A+!

[MusicMaker]

Thanks!

I did some calculations. Assuming 3/4" construction.

I used several cabinet makers to determine the internal volume of each maker.

From Thiele Small parameters it seems that a 2.0 cu ft internal space is 'best' or 'ideal' for a 12" speaker (but take that with a grain of salt.) There are 'other' considerations such as resonant Hz of the speaker and whether the box is 'ported' or 'closed'.

I believe HAD calculated the size of his port based upon the TS parameters.

If you consider porting to be 'just a hole', then a 3/4" deep hole by N x N "looks" like a port to the speaker, just as a 3" dia X 7" port does.

Notice the different sizes? It would be interesting to load these boxes and test the differences.

The 'Bills' Forte was from a guy who was selling one. I asked for dimensions. His port was different than what I extrapolated for a Forte cab drawing I found that gave outside dimensions. Being that Forte milled out a good part of the inside I suspect my inside volume to be larger than shown.

Forte: http://thaddeushogarth.berkleemusicblog ... one-in-3d/

NOTE: the EVL12 is also 'ported' with an adjustable port. http://s1113.photobucket.com/user/steve ... 6.jpg.html

[MusicMaker]

Busy couple of weeks. Finally, I got some free time to test with the light bulb limiter.

Here are the results:

40W bulb.

I would first measure the power supply voltages without tubes plugged in.

Red/Red 561 vac
red 282.5 vac to ground
red 282.5 vac to ground

Green/green 5.84vac
Red/Blue 51.5 vac
Red/Orange is ground

Check plate voltages (they will be higher due to no loading.)

V4 - V7 376vdc off standby

You can start with a 25w or 40w light bulb and it limits the current to the amp.
On power up the reservoir caps charge and after a brief flash (main caps charge) then the glow will lessen.

Flip it off standby, it should brighten momentarily again then go to a lower glow.

Slight glow, but no 'lessening' of glow until I took off standby, then a bright glow and then went dim glow as before standby was on.

If it stays bright, there is a problem.
If you really want to be sure, then step up to a 60 watt bulb.

60W bulb

Red/Red 607 vac
Red 302 to ground
Red 302 to ground

Green/Green 6.1 vac
Red/Blue 55.8 vac

V4 - V7 412vdc off standby


No smoke! Thank you Structo! (Tom)

Do the numbers jive?? Any other tests I need to do?



Ordered tubes from Antique Supply. Should arrive next week sometime.

[aflynt]

Thanks!

I did some calculations. Assuming 3/4" construction.

I used several cabinet makers to determine the internal volume of each maker.

From Thiele Small parameters it seems that a 2.0 cu ft internal space is 'best' or 'ideal' for a 12" speaker (but take that with a grain of salt.) There are 'other' considerations such as resonant Hz of the speaker and whether the box is 'ported' or 'closed'.

I believe HAD calculated the size of his port based upon the TS parameters.

If you consider porting to be 'just a hole', then a 3/4" deep hole by N x N "looks" like a port to the speaker, just as a 3" dia X 7" port does.

Notice the different sizes? It would be interesting to load these boxes and test the differences.

The 'Bills' Forte was from a guy who was selling one. I asked for dimensions. His port was different than what I extrapolated for a Forte cab drawing I found that gave outside dimensions. Being that Forte milled out a good part of the inside I suspect my inside volume to be larger than shown.

Forte: http://thaddeushogarth.berkleemusicblog ... one-in-3d/

NOTE: the EVL12 is also 'ported' with an adjustable port. http://s1113.photobucket.com/user/steve ... 6.jpg.html

My 2 Forte 3D 1x12s are 14" deep x 16" tall by 22" wide on the outside. Inner dimensions 20.5" wide x 14.5" tall x 10" deep. Ports are 12" tall x 4" wide ovals on either side. I've taken some pictures of the inner construction with the 3/4" wide by 1/2" deep milled channels and composite "honeycomb" deflector baffles.

-Aaron

[aflynt]

Busy couple of weeks. Finally, I got some free time to test with the light bulb limiter.

Here are the results:

40W bulb.

I would first measure the power supply voltages without tubes plugged in.

Red/Red 561 vac
red 282.5 vac to ground
red 282.5 vac to ground

Green/green 5.84vac
Red/Blue 51.5 vac
Red/Orange is ground

Check plate voltages (they will be higher due to no loading.)

V4 - V7 376vdc off standby

You can start with a 25w or 40w light bulb and it limits the current to the amp.
On power up the reservoir caps charge and after a brief flash (main caps charge) then the glow will lessen.

Flip it off standby, it should brighten momentarily again then go to a lower glow.

Slight glow, but no 'lessening' of glow until I took off standby, then a bright glow and then went dim glow as before standby was on.

If it stays bright, there is a problem.
If you really want to be sure, then step up to a 60 watt bulb.

60W bulb

Red/Red 607 vac
Red 302 to ground
Red 302 to ground

Green/Green 6.1 vac
Red/Blue 55.8 vac

V4 - V7 412vdc off standby


No smoke! Thank you Structo! (Tom)

Do the numbers jive?? Any other tests I need to do?



Ordered tubes from Antique Supply. Should arrive next week sometime.

I'd measure the voltages without the bulb then since it didn't blow up or anything. I usually take it up gradually with a variac the first time with the voltmeter between GND and B+1.

-Aaron

[MusicMaker]

I think my electronic junkyard might have a variac? How is it used? Reasoning? (or point me to a link?)

Would I need a 4A or would a 3A do?


Aflynt your Forte cab measurements, you said the inside was 10" from a 14" depth. I calculate 12.5 if the sides are 3/4" thick.

Just curious how do you like the Forte?

Thanks for the input.

[aflynt]

I think my electronic junkyard might have a variac? How is it used? Reasoning? (or point me to a link?)

Would I need a 4A or would a 3A do?


Aflynt your Forte cab measurements, you said the inside was 10" from a 14" depth. I calculate 12.5 if the sides are 3/4" thick.

Just curious how do you like the Forte?

Thanks for the input.

I don't have any incandescent bulbs so I just use the variac to lower the voltage. It goes between the amp and the wall. 3 amp should do fine.

I love the Forte 3D 1x12". I've got 2. Depending on the situation I'll use one or both. I measured the inside of the cleats, so that's probably why I came up short of your calculation. Lots of weird nooks and crannies inside that thing. Not sure how you would come up with a good volume measurement.

-Aaron

[martin manning]

If you have powered it up with a limiter and see no indication of excessive current draw, you can apply full line voltage. I would do that, remeasure the plate, screen, and filament voltages, and also check the bias voltage and range by measuring it at the output tube pin 5's. Get readings there with the bias trimmer set at its two extremes, and leave it positioned for minimum (most negative) voltage.

When you install tubes, be sure to connect a speaker or dummy load, and use the limiter for the first power up to be sure that there is still no high current draw. Don't bother with measurements yet. If things look good, remove the limiter, apply full line voltage, and set the output tube bias. Then you can get some actual operating voltages. Let it idle for 15-20 minutes and remeasure to see if it is stable.

A bulb limiter is better than a Variac for this purpose since it limits current flow to the nominal maximum that the bulb uses if there is a short in the amp. For example, using a 60W bulb the current is limited to 60W/120V = 500mA.

[MusicMaker]

I think my electronic junkyard might have a variac? How is it used? Reasoning? (or point me to a link?)

Would I need a 4A or would a 3A do?


Aflynt your Forte cab measurements, you said the inside was 10" from a 14" depth. I calculate 12.5 if the sides are 3/4" thick.

Just curious how do you like the Forte?

Thanks for the input.

I don't have any incandescent bulbs so I just use the variac to lower the voltage. It goes between the amp and the wall. 3 amp should do fine.

I love the Forte 3D 1x12". I've got 2. Depending on the situation I'll use one or both. I measured the inside of the cleats, so that's probably why I came up short of your calculation. Lots of weird nooks and crannies inside that thing. Not sure how you would come up with a good volume measurement.

-Aaron

Integral Calculus could do it. Not so good with calc myself, so I would opt for the easier measure the length of the slots. Figure out the volume LxWxH and the area of the circle = Pr^2 for each unique slot. Multiply that times all the similar slots. Add them up and include that area in the total I figured. There would be some 'assumptions' that the baffles occupy some space.

Rough numbers: Forte's volume is @ 3716, Dumbles @ 3850. A SWAG would get you in the ball park: I'm guessing Forte's is pretty close to Dumble's?

Dumble's port is 53.69, or 54 cu in (3/4" depth)
Forte's port is 51.85, or 52 cu in (3/4" depth) that includes 2 ports.

If you "fold" them in half, you double the depth to 1.5", do it again and you get 3" depth. But you have to use sq in, not cu in to 'fold' them.

Dumble is 71.59, or 72 sq in folded in half you half the 72 = 36 sq in x 1.5" deep.
then 18 sq in x 3" deep,
then a 9 sq in x 6" deep port would act like Dumble's back port.

Forte is 34.75 x 2 = 69.5 sq in etc....

[MusicMaker]

If you have powered it up with a limiter and see no indication of excessive current draw, you can apply full line voltage. I would do that,
remeasure the plate, screen, and filament voltages, and also check the bias voltage and range by measuring it at the output tube pin 5's.
Get readings there with the bias trimmer set at its two extremes, and leave it positioned for minimum (most negative) voltage.

Ok, let's see if I read this correctly... meter set for DC


Full power

B+1 = 463
B+2 = 463
B+3 = 452
B+4 = 380
B+5 = 374

Bias = -38 to -63.7

Set at -38


Output tube

pin2 heater = 6.40
pin3 plate = 463
pin4 grid #2 = 464
pin5 grid #1 = -38.20
pin7 heater = 5.50


12AX7s

V1
Section 2
pin1 plate = 366
pin2 cathode = 0
pin3 grid = fluctuating mV voltage (felt like a cap was charging)

Section 1
pin6 grid = 367
pin7 cathode = 0
pin8 plate = fluctuating mV voltage


V2
Section 2
pin1 plate = 373
pin2 cathode = 0
pin3 grid = fluctuating mV voltage

Section 1
pin6 grid = 374
pin7 cathode = 0
pin8 plate = 0


V3
Section 2
pin1 plate = 448
pin2 cathode = 0
pin3 grid = fluctuating mV voltage

Section 1
pin6 grid = 446
pin7 cathode = 0
pin8 plate = luctuating mV voltage

I think I measured correctly, please tell me if I didn't.

no smoke...

[martin manning]

First, set the bias trimmer to minimum (most negative) voltage, -64V.

B+ voltages look good.

The heater voltages on output tube pins 2 and 7 look strange. Are you measuring AC to ground? I'd expect ~3.4-3.5VAC, and matching values on those two pins.

Voltages on the preamp tubes look good if the pin designations (not the electrode names you listed) are correct. 1, 2, 3, and 6, 7, 8 are plate, grid, and cathode respectively.

How about the relay supply voltage? Can you get the relays to pull in with the panel and foot switches?

[MusicMaker]

Thanks Martin!

First, set the bias trimmer to minimum (most negative) voltage, -64V.

B+ voltages look good.

The heater voltages on output tube pins 2 and 7 look strange. Are you measuring AC to ground? I'd expect ~3.4-3.5VAC, and matching values on those two pins.

Had meter on DC! I just measured p4 123Vac and p9 128Vac??? That's a bit odd! I have both green wires (which the MM PT spec sheet indicates 6.5v @5.5A) connected to p2&7 on V7. (see pic).

http://www.classictone.net/40-18004.pdf

Voltages on the preamp tubes look good if the pin designations (not the electrode names you listed) are correct. 1, 2, 3, and 6, 7, 8 are plate, grid, and cathode respectively.

You are correct. Pins are correct. I was referring to the wrong layout.
Searching "12AX7 pinout" doesn't necessarily bring up that pinout! Best to leave off "pinout" in search parameters!

How about the relay supply voltage? Can you get the relays to pull in with the panel and foot switches?

Relays do not pull in. I have @ 12v to each. See pics. I may have the foot pedal sw upside down? Wires are correct from relay to switches. see pics for comments.