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Old 20th September 2013, 02:35 AM   #1
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Default CRITIQUE MY 5F1 BUILD?

But be gentle..... it's my FIRST tube amp. Not as quiet as I'd like, but hope my next amp is better (a Deluxe). Separate supply chassis, the cab is a cheapo Squire. Can't put a better spkr in it, 6V6 barely clears the magnet. Note the bridge rectifier, to save space (and a tube) and take advantage of the less $$ Weber WRVBPT. I puts 340V to the 6V6 plate, and 205 to the AX7 (by tweaking the B+ resistors). Put a "clean/dirty" 50K pot on the rear - adds to the 22K NFB for more breakup (clipping). Was built with budget in mind (chassis are salvage electronics, homemade eyelet bd). Get 13+ watts of plate dissipation. Still need a pilot lite (LED w/diode and resistor off filament AC), and a faceplate. Any comment on improvements are appreciated! Thanks for viewing- Jeff
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Old 20th September 2013, 05:09 PM   #2
shanx is offline shanx  Canada
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Hi Jeff, Nice build, congrats! Just a comment from me, for 340V and 13+ watts plate dissipation you will probably be OK with the JJ tube you have (6V6 S, I think?) and a couple of other brands. Having said that, there are some other ones where it would be over their rated max plate volts and dissipation. How do you like the variable NFB ?
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Old 20th September 2013, 07:20 PM   #3
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Thanks Shanx! I like what the adjustable NFB does - wth it stock at 22K the amp on a scope had a perfect sine wave up to max vol, but I wanted some clipping (breakup). Planned on adjusting preamp cathode resistance and/or plate voltage (the 6V6 was running very warm, and didn't want to push it any further), or the NFB. Played with the NFB first, and got what I wanted there, it didn't change any tube voltages (bias), but couldn't decide on what fixed setting I wanted, so put the pot in. There is only a bit of increased volume (meaning more plate current), but can adjust the breakup point now.
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Old 20th September 2013, 08:19 PM   #4
shanx is offline shanx  Canada
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Glad to hear it sounds good. The high plate volts give you that clean headroom, so running with less NFB gets you some nice breakup. A dropping resistor in the power supply may be a suggestion as to get your plate voltage down as well. A tube rectifier would have knocked the available plate volts down quite a bit, but a few tricks could be done with diodes and a dropping resistor... and give you a bit of that sagging effect. Hope you have fun with it!
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Old 20th September 2013, 09:10 PM   #5
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I used a bridge rectifier to get as much B+ out of the PT as I could. The Weber has no CT (so can't use a tube/full wave), and is only 260 VAC. My stock Fender Champ has over 400VDC on its plate (and has ran great for years - has a good NOS 6V6). My next build will be an early Deluxe - not sure if I want to run a paraphase or long-tail PI - and have a good PT and 5Y3 or GZ34 for it.....
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Old 21st September 2013, 05:49 PM   #6
Tarzan is offline Tarzan  Belgium
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Hi LATUBEGEEK ,
Tell me, what can we find on the terminals of the power supply module?
If there is any voltage at all and mains in particular; get it protected by a plastic cover or something.
Did you grounded both modules to the safety ground?
The 6V6 is very close to the magnet of the speaker. Hopefullly it will not shorten the life of the 6V6.
The heater wiring needs some more attention.
You mention it is not as quit as you like. Is there any hum?
Look at the heater wiring...
For a first effort; Well done.
And welcome in the club
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Old 21st September 2013, 07:37 PM   #7
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Tarzan - Thanks for the positive critique! Yeah, there's 117VAC, B+ and 6.3VAC on the PS, should be covered. And I did ground both chassis to the green wire to the AC cord gnd. And I had been warned about the 6V6 being too near the spkr, but wasn't sure what the effect would be. Now I do! And.... I knew I might have lacing and grounding improvements to make.... still not sure what a "star" ground setup is, if I should use a brass plate, twist wires, etc. Grounding got rid of some hum, and plugging the guitar in gets rid of most of the rest, but with no input there's no hum at vol=0, but goes up when volume does. Have found layout diagrams from other builders, will learn from them. Thanks again Jeff
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Old 21st September 2013, 11:50 PM   #8
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Quote:
Originally Posted by LATUBEGEEK View Post
I used a bridge rectifier to get as much B+ out of the PT as I could. The Weber has no CT (so can't use a tube/full wave), and is only 260 VAC. My stock Fender Champ has over 400VDC on its plate (and has ran great for years - has a good NOS 6V6). My next build will be an early Deluxe - not sure if I want to run a paraphase or long-tail PI - and have a good PT and 5Y3 or GZ34 for it.....
Funny you should mention it, not suggesting doing it as it can be tricky to do the wire routing and not get any oscillations at high gain but...

Click the image to open in full size.

Tremolux 5E9a paraphase to 5G9 LTP

... using a four pole two position switch. Could leave out the fixed bias option and do it with a three pole switch.

Last edited by Printer2; 21st September 2013 at 11:52 PM.
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Old 25th September 2013, 06:52 PM   #9
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Wow what a cool option! My first thought would be to breadboard it, but I've had terrible luck keeping breadboard circuits from oscillating - lacing and grounding gets compromised, and I can't see the signal on my scope with all the oscillating - which is the whole purpose of experimenting before building. I've thought of building the breadboard as close to a final build as I can, to clean things up. My pic below is for a 5F1 setup - could only use it to adjust resistors and change voltages - couldn't see a clean enough sine wave to see breakup! Also, I have a lot to learn about PIs. Below is an old stock PA I've been playing with: 3 12SJ7 pentode preamp tubes (with DC filaments), 2 6L6 p-p, and a PI I haven't figured out. Had no schematic, drew it out as I saw it, and have started to redraw it so I can compare it to conventional schematics. Is plenty loud right now, but I could replace those preamp tubes with 12SL7s (hi-u twin triodes) and LOOK OUT! Thanks Jeff
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Old 10th November 2013, 05:05 PM   #10
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Great looking turret board but I believe some of the power supply wiring could have been shortened a bit to minimize hum and noise, but if it works, dont fix it... Also, the variable NFB is a great option to have.
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