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Old 28th December 2012, 03:50 AM   #51
pso is offline pso  Spain
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Think the same.
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Old 28th December 2012, 04:01 AM   #52
tomchr is offline tomchr  United States
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Default 300B Amp - Driver Board BOM

Bill of materials for the 300B Amp Driver Board is attached.

Of the three options (6N6P, ECC99, and 12BH7A) the 6N6P and ECC99 options are well tested. I tried the 12BH7A as well (using two 6.2 V zeners in series for the cathode bias and 10 mA anode current) but ended up preferring the 6N6P. I didn't play as much with the 12BH7A, but I think I arrived at a pretty good operating point. If you prefer a more colored sound, I suggest trying the 12BH7A. I prefer a cleaner sound, hence, would choose the 6N6P (or ECC99).

Note that to change from 6N6P to ECC99 or 12BH7A, the options OPT1A,B and OPT2A,B need to change as follows:
- When using 6N6P, connect OPT1B with a wire jumper. Connect OPT2B with a wire jumper.
- When using ECC99 or 12BH7A, connect OPT1A with a wire jumper. Connect OPT2A with a wire jumper.
These options change the heater connections. The heater voltage is 6.3 V for all options. After assembly, you can verify that you've got the options set correctly by measuring the heater voltages at pins 4, 5, and 9. Consult with the data sheet for the tube of your choice to ensure that you've got it connected correctly.

~Tom
Attached Files
File Type: pdf 300B_Amp_DriverBoard_SchematicBOM.pdf (161.4 KB, 182 views)
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21st Century Maida Regulator, Universal Filament Regulator, Damn Good 300B, Novar Spud, and more...
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Last edited by tomchr; 28th December 2012 at 04:03 AM.
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Old 31st December 2012, 11:20 AM   #53
VT67 is offline VT67  Belgium
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I'm tempted to give this project a go because I still have a pair of 300BXLS and some 6N6P's. Any output transformer you favor for this amp? I'm trying to figure out the cost for the whole amp. For the moment I'm busy to see if all the parts are also available at Mouser. Hate Digi-Key, way to expensive (customs and s..t)

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Old 31st December 2012, 08:54 PM   #54
tomchr is offline tomchr  United States
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The parts are pretty generic and should be available world-wide. I would think Farnell in Europe would be able to help you out. The only tricky part is the LT3092 as it is available in many different packages. You want the SOT-223 version.

I've used the Edcor CXSE25-8-5k and Electra-Print 300B, 100 mA, 5 kOhm primary, 4 & 8 ohm secondary, copper wire with this amp. The Edcors are quite nice. At about $80/each they're incredible bang for the buck. I went with the Electra-Print transformers because I needed the dual secondary and wanted to try Jack's transformers. I am very pleased with the transformers I got. I like the tone and the detail in both the highs and lows. The Edcor is spec'ed to 50 Hz, the E-P 25 Hz. So you get an extra octave... But the E-P is also about 3x the cost of the Edcor. Tradeoffs, tradeoffs...

~Tom
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Old 2nd January 2013, 11:47 AM   #55
VT67 is offline VT67  Belgium
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As for the output transformers, the Hammond 1628SEA from Tube-Town in Germany are the most economical for me at 144 ($191)a pop.
The LT3080 and LT3092 in the desired packages I could get from Arrow Electronics.

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Old 14th January 2013, 02:25 AM   #56
tomchr is offline tomchr  United States
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It's amazing what a 15-cent ferrite bead can do for you... I have ironed the last kink out of the power supply.

To ensure stability of the bias regulator, Q1, a Bourns FB43-100 ferrite bead should be added to the gate lead of Q1. That's Digikey P/N M8702-ND.

If a ferrite bead isn't available in your local market, use a 10 nF, 50 V ceramic capacitor from Q1 gate to Q1 source (pins 1 and 3).

I've updated the schematic and BOM to reflect this.

~Tom
Attached Files
File Type: pdf 300B_PSU_2P01_SchematicBOM.pdf (99.9 KB, 95 views)
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Old 14th January 2013, 04:54 AM   #57
grufti is offline grufti  United States
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Tom, can you post some more pictures of your latest and greatest versions? I just checked the datasheets of the Bourns FB-43-100-RC ferrite bead and the Fairchild FQP3P50 transistor. It seems that the bead will only fit over the lower part of the transistors leg and I didn't think that part was exposed [for the bead to go over it]. I have a few other such build oriented questions on my mind that would probably be resolved by looking at pictures from other angles. No need to rush into action. I am busy with other stuff and can't start my build quite yet. Thinking about it nonetheless.
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Old 14th January 2013, 06:58 PM   #58
tomchr is offline tomchr  United States
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Q1 is in a TO-220 package and it's sitting on a little heat sink. I purposely designed the footprint for the Q1-heatsink combo such that you bend the leads on Q1 just after they go from wide to skinny (i.e. you bend the skinny part to form a 90 degree angle).

I measured a couple of TO-220 packages. When adding the thickness of the heat sink, there ends up being 4.6 mm from the bottom of the transistor lead to the top of the PCB. This is enough for the ferrite bead. And as the bend on the lead is on the skinny part, the ferrite drapes over just fine. The ferrite sits vertically between the PCB and the flat part of the TO-220 lead.

I hope this makes sense. I'll follow up with pictures in a few days. Thanks for the questions, by the way. It's important to me that people are able to assemble the amp successfully. Your questions will help me improve the overall quality of my project documentation. Thanks.

~Tom
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Last edited by tomchr; 14th January 2013 at 07:02 PM.
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Old 15th January 2013, 02:42 PM   #59
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There is no problem in running the two 5V filaments from the same winding? as it is qualified only for 2A.
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Old 15th January 2013, 07:43 PM   #60
tomchr is offline tomchr  United States
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The ClassicTone 40-18069 power transformer has two 15 V windings, each rated for 2 A. Recall, I'm using my Universal Filament Regulators to power the 300B and 6N6P filaments. The Universal Filament Regulators are switching regulators and they are very efficient (~90 %). So Power In = 1.1 * Power Out. Give or take...

Hence, each 300B filament regulator only draws 1.4*5*1.1 = 7.7 W from the transformer. 7.7 * 2 = 15.4 W. The winding is rated for 15 * 2 = 30 W, so there's plenty of margin.

The worst case condition on the 6.3 V supply is when you're using ECC99s as they draw about 1.8 A total. So 6.3 * 1.8 * 1.1 = 12.5 W drawn from the transformer. Still... Pretty far below 30 W.

Note, that the RMS current drawn by the rectifier is quite a bit higher than that drawn by the load. This is due to the way full-wave rectifiers work. They draw the current in pulses so the peak current is quite high. I ran extensive simulations on all the supplies to ensure that the transformer windings were not overloaded. I have verified the validity of my sims in my prototype. The transformer is running at around 80 % of full capacity. It gets lukewarm (maybe 35~40 deg C). That's still well within the range of normal.

Of course, if you're using linear regulators, you won't be able to use the ClassicTone 40-18069 transformer -- at least not to supply the filament supplies. That would also result in some ungodly amount of power dissipated in the filament regulators. That's why I went with switching regulators in the first place. If you insist on using linear regulators, you're probably better off using a separate transformer for the filament supplies. Something like an 2 x 8 V, 50 VA tranny should work, but you'll have to do your own design there.

~Tom
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