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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Thu May 12, 2011 11:10 am
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Great to hear it's all finished and sounds great! The orange caps sure do make it a bright amp. It really puts your tone knob to use on the guitar. 8)

I look forward to hearing some demos of the amp. Speaking of, I need to get some more up having read the previous comment about there not being enough.

I can honestly say, having built the same amp down to every detail except the tone pot cap being an orange drop on mine, the amp stays pretty bright and has lots of drive. I don't think you'll ever have a problem cutting through in a band mix with this one. I know I don't. :D For 18 watts, these things get loud and have some honk to them.

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 7:19 pm
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Just a few pics of my finished build.

Ross


Image

Image

Image

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 7:56 pm
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Sweet! I like that darker color. How do you like the mallory 150s? They've got a smooth high end.

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 8:41 pm
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Thanks, rjake. It ended up darker than I'd intended. It finally became a matter of trying to get something close to even, regardless of color. But I'm okay with it. It kind of looks like an lacquered suitcase from the '40s, and it doesn't look like every other 5e3 out there. The ten coats of nitro helped a lot in giving it a more polished appearance.

I wish I could give you a meaningful report on the sound of the Mallory caps. Unfortunately, I don't have anything to compare them to, and, honestly, I don't have the best ear for such things. I'm still trying to detect the difference between a 12AX7 and a 12AY7 in V1 and wondering whether swapping in a Texas Heat speaker will make an improvement that even I can hear.

I think my voltages are running a bit high, but I'm not sure what to do about it. As far as I know, the biggest problem this presents is that I'll run through tubes faster than otherwise. I know Snowy did some magic with diodes to bring his voltages down, but I wouldn't know where to start.

My biggest problem, though, is what to do now. I can't afford to build another one. :-)

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 8:51 pm
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Funny story: After the dim-bulb tests, I went to the do the power-up test sequence detailed in the build manual. Between the stiff, new tube sockets and my inexperience with tubes, I managed to crack the rectifier tube. At that point there was no way I was going to wait days to have a new tube shipped to me, so I headed to Guitar Center for an overpriced Mesa Boogie GZ34.

On my way to Guitar Center, I realized I was driving past Fry's Electronics. They have electronic components, right? Cheap, too. So I stopped, went to the electronic components desk and asked where their vacuum tubes were. The young guy tried to direct me to the appliance department, where they sell vacuum cleaners. "No, it's an electronic component." He led me over to shelves where they had conduit and tubing for electronics projects. "No, no, it's an electronic component! Like a transistor, but before they had transistors. You know, in amplifier circuits?" He quite literally had never heard of such a thing. Neither had the only other guy working in the components department.

These kids today, I tell ya.

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 8:58 pm
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The 12AX7 or 12AY7 is definitely a tone to taste thing. The old ones had the 12AY7 in them, so Leo thought it was cool. The Pro I built currently has 12AY7>12AY7>12AX7 that I like, but when I did a demo for a guy, he preferred all 12AX7s. To each his own. IMO I think the 12AY7's give the overdrive more balance between the preamp and power amp.

What are your voltages?

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 10:17 pm
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During the power-up tests, the build manual has you check B+ (at the positive side of C12, one of the filter caps) against chassis ground with only the rectifier tube inserted. The manual spec is 460V±10V. Mine measured 519V.

Now, with a full complement of tubes, B+ measured at that location and at pin 8 of the rectifier tube is a steady 440V. I get the sense that this is high for this amp.

Of course there is a lot of info on the Web about these issues, but most assume a stock 5e3 build. The Tube Depot kit, however, uses a beefier power transformer spec'ed for a Deluxe Reverb and a different rectifier to match (GZ34/5AR4), so I don't know how much of the common info applies.

Thanks,
Ross

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 10:36 pm
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If I'm measuring them correctly (pin 3 of the 6V6 to chassis ground), the plate voltage on the power tubes is 436V and 438V.

Ross

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 11:07 pm
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Those JJ tubes are not your normal 6V6 and are good to 500 volts. I think you'll be fine.

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 11:35 pm
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Thanks for the encouragement, rjake.

I wanted to use Snowy's method of calculating idle dissipation per power tube described earlier in the thread, but I can't figure out how to measure the screen current. Based on info found elsewhere, I tried to use this calculation:

((B+) - (pin 4 to ground))/1500 = screen current
(444 - 395)/1500 = 0.033 or 33 ma

but that seems too high.

Ross

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 11:40 pm
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I just noticed something in your pics. The color code doesn't look correct on your 3 watt resistor between the F&T caps or maybe I'm seeing things. It should be 4.7K ohms. You might stick a meter on that to verify, no power to the amp of course.

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sat May 14, 2011 11:50 pm
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Ross, the amp looks great I reckon. The darker colour gives it a real 1957 vintage vibe.

The 6v6 JJ's are a really tough tube they can really take some punishment, in an ideal world you may opt to try to getting the idle dissipation under 14 watts. It's a Cathode biased amp so the 70% rule at idle doesn't apply.

If you plug your voltages into the post I made previously, can you work out the dissipation?

Or if you like, post them in here using the steps in my post and I can work through it and lay it out for you.

To drop the voltages you can put a few 15volt / 5 Watt Zener diodes (Cathodes pointing to ground) in series between the PT Centre tap and ground (that's the Red/Yellow Stripe wire thats going to ground). This can can be used to drop the B+ and get the dissipation to where you (and the tubes) are more comfortable. I can give you details on how to set that up if you want to do it. I'll try to find a pic of my setup, I know I took one.

Edit:
Here's the Zener string I set up. 4 x 15 Volt and 2 x 12 Volt Zeners in series with the PT Centre Tap to ground. All 5 Watt rated.
Image

As rjake points out those JJ's can take a lot of abuse.


Snowy


Last edited by No457 Snowy on Thu Dec 13, 2012 2:23 pm, edited 5 times in total.

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sun May 15, 2011 12:12 am
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Here's how to calculate the screen current on the amp. (using my measurements)

Voltage drop across 22k resistor (R22) divided by the actual measured resistance (22000)
= current of the 2 preamp tubes, my measurements are as follows.
88 volts divided by 22000 = 0.004 (4ma)


Voltage drop across 4.7k resistor (R21) divided by the actual measured resistance (4630)
= total of power tube screen current and current in preamp tubes, my measurements are as follows.
34.8 volts divided by 4630 = 0.0075 (7.5ma)

So to find the actual screen current on the power tubes you need to subtract the preamp tube current you measured on R22 from the total screen currents and preamp tube current you measured on R21. The number left over is the power tube screen current.

= 7.5ma (R21) - 4ma (R22) = 3.5ma (Power tube screen current)

Congrats on the build, so how is the amp sounding?

Snowy


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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sun May 15, 2011 7:12 am
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The darker shade looks good! Like it's been thru a lot of play in a smoky bar...

I'm curious to what you find with the voltages and if they should be stepped down. Looks like you're not that far off though with the +/- 10%.

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Post subject: Re: Let's build another Tweed Deluxe Amp!
Posted: Sun May 15, 2011 9:51 am
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rjake,

Thanks for looking at it. The 4.7K resistor off the filter caps tests right at spec. (I don't trust my own reading of resistor codes, so I tested each one immediately prior to mounting.)

Snowy,

Thank you very much. That was exactly the info I needed to run the calculations. The idle dissipation of my power tubes is 19.1V (calculations below). It looks like I'm going to be trying to find a terminal strip and some diodes. (Can anyone recommend a source? I'm not seeing a nifty one-screw board like Snowy's anywhere.) Can you offer guidance on values? I don't know whether your 4 x 15 volt and 2 x 12 volt configuration is right for my numbers. Is there a reason you used six smaller-value diodes, rather than a single larger one? Better heat dissipation, perhaps?

I'm enjoying the sound of the amp, but I'm still getting used to it. Great dynamics, amazing touch sensitivity, fairly creamy overdrive with more than a little growl. A tendency to get very boomy on bass notes. It seems to prefer single-coil pickups.

It probably sounds best with my Telecaster with Fender Noiseless Pickups. With my Les Paul (actually a Tradition S2000 LP copy) it's pretty much pure '70s hard rock/Southern rock. With my Levinson Blade Strat, I can get some nice tones, but there are some settings that just sound dead, and I have to watch out for ice-pick tones. With my Epiphone Sheraton II, I have to crank the guitar volume way down to keep the amp from being ridiculously overdriven. In general humbuckers seem to be more of a challenge with this amp.

I really can't thank you enough for your posts. I probably wouldn't have tackled this project without your first build diary thread. During my build there were several points where the manual was unclear or inconsistent, and your amazing pictures led me in the right direction.

Ross


Voltage across Cathode Resistor = 25.45 volts
Actual Measured Resistance of Cathode Resistor = 257.6 Ohms
Plate Voltage (Pin3 to Ground) = 436 volts

Plate Current calculations:
Cathode Resistor Voltage (25.45 volts) / Cathode Resistor Ohms (257.6) = 0.099 (99 milliamps)
This is the Cathode Current (including screen current) for BOTH Tubes.
Subtract the screen current (measured to be 6.0ma) = 93.0ma
Divided by 2 (tubes) = 46.50ma Plate Current per tube

Idle Dissipation calculations:
Plate Voltage (436 volts) - Cathode Resistor Voltage (25.45 volts) = 410.6 volts
multiplied by Plate Current (0.04650ma) = 19.1 watts

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