Author Topic: My DIY TUBE Projects (Read 13093 times)

stick · « **Reply #30 on:** Mar 29, 2012 at 07:37 PM »

Quote from: TonyT on Mar 16, 2012 at 06:43 PM

the pleasure is mine, if you have anything on your mind, just ask and we will sort it out...

I have a question on how to put a headphone out on a tube preamp. my headphone is 32 ohms... and my preamp is a cathode follower 12au7 (1 tube/ch). can i connect it directly on the preamp out?

ATJr. · « **Reply #31 on:** Mar 29, 2012 at 07:48 PM »

the output impedance of the 12au7 is a bit high to feed the headphone directly, the 6dj8 might do it owing to its highish transconductance....

if you are not adverse to mosfets, a mosfet follower will also do it...

stick · « **Reply #32 on:** Mar 30, 2012 at 05:27 PM »

^ Thanks...

ATJr. · « **Reply #33 on:** Mar 30, 2012 at 05:33 PM »

stick, paki remind si edrel sa mga order kong end bells at bobbin....

stick · « **Reply #34 on:** Mar 31, 2012 at 11:49 AM »

^ok, no problem...

I'm starting with a new diy project! its the 832 Tube... hope this tube would sound nice... most materials used for chasis made from scrap bakelite,acrylic, aluminum, binding post, others parts are NOS..

ATJr. · « **Reply #35 on:** Mar 31, 2012 at 11:58 AM »

here is a good read: http://www.kaponk.com/~yanyong/ETF06TS.pdf

stick · « **Reply #36 on:** Apr 01, 2012 at 10:18 AM »

^ Thanks for the link for this document... i'll try it someday... i'm still busy with a couple of projects... including a TA8252HQ BTL car audio power amplifier (37Wx4) i have a dozen of this chips... I plan to use it as BI-AMP on a stereo set-up... still looking for good filter ether active or passive...

stick · « **Reply #37 on:** Apr 05, 2012 at 12:58 PM »

done with the 832 push pull amp using schematic from http://www.audiohobbyist.com/projects/832.htm...

sound ok but we totally omitted the feedback circuit since it introduces low frequency oscillation... still finding answers on this phenomenon... anyone knows? any ideas would greatly help... now we easily get distortion and clipping without the feedback at higher volumes...

Also power traffo gets too hot... maybe due to the low voltage reading from heaters... (just a hunch) because heater supply is ok without load producing 6.3X Volts but with load voltage drops to 5.86 Volts... other modifications are: used tube rectifier, B+ choke, cathode resistor increase to 330 ohms..

ATJr. · « **Reply #38 on:** Apr 05, 2012 at 01:12 PM »

baligtarin mo yung hot at ground ng output secondary mo, para tama ang phasing......motorboating is a sign of incorrect phasing of the output secondary....wala nito sa set, dahil hindi nagamit ng feedback...
tubes rated for 6.3 can work fine at filament voltages between 5.9 to 6.9.....

you can also try to regulate the screen voltage to 200volts using a string of zeners and then you can raise the plate supply to more than 350volts for more power.....

post ka ng pics.....

stick · « **Reply #39 on:** Apr 07, 2012 at 07:30 AM »

^ Thanks, will try this solution soon... I only checked the B+ and its at 268V. will also check other voltages...

ATJr. · « **Reply #40 on:** Apr 07, 2012 at 10:18 AM »

the 832 and its bigger brother the 829 can take higher plate voltages if you keep a close eye on the screen grid voltage...

stick · « **Reply #41 on:** Apr 14, 2012 at 06:20 PM »

Quote from: TonyT on Apr 05, 2012 at 01:12 PM

baligtarin mo yung hot at ground ng output secondary mo, para tama ang phasing......motorboating is a sign of incorrect phasing of the output secondary....wala nito sa set, dahil hindi nagamit ng feedback...

Had the chance to reverse the hot and ground terminals of the secondary and it worked with the feedback... your the man Tony!... hope to learn from you more...

Quote from: TonyT on Apr 05, 2012 at 01:12 PM

you can also try to regulate the screen voltage to 200volts using a string of zeners and then you can raise the plate supply to more than 350volts for more power.....

Now its time to try this string of zeners... what value can I use? I'm not that familiar with zeners of high voltages... I only know of the 5~12v zeners...

Quote from: TonyT on Apr 07, 2012 at 10:18 AM

the 832 and its bigger brother the 829 can take higher plate voltages if you keep a close eye on the screen grid voltage...

I had the chance to try this on the same circuit above... but I like the sound of the RCA 832 much more...

ATJr. · « **Reply #42 on:** Apr 15, 2012 at 06:53 AM »

Quote

Had the chance to reverse the hot and ground terminals of the secondary and it worked with the feedback...

since you are not doing unltra-linear with this amp, another way is by swapping the plate leads on the primary side of the traffo

Quote

Now its time to try this string of zeners... what value can I use? I'm not that familiar with zeners of high voltages... I only know of the 5~12v zeners...

this is Pete Millet's power amp using tv tubes,

regulator Q1 is the source follower using zener string as reference, you ca add more zeners to get the required voltage, you may use 2SK3563 mosfets, available at newport electronics, it is fully encapsulted...

notice that Q2 forms a capacitor multiplier circuit, for Class AB, i do not think that cap multiplier is necessary specially for push pull outputs:

Quote

I had the chance to try this on the same circuit above... but I like the sound of the RCA 832 much more...

829b is capable of 40watts combined plate while the 832 is good for only 20 watts plates, to whip the 829b's you will need higher bias operating points.....they are not a drop in replacement that you can just plug-in without doing anything on the circuit...

lastly, i invite you to join us here: http://www.electronicslab.ph/forum/index.php?topic=25478.msg618676#new

stick · « **Reply #43 on:** Nov 08, 2012 at 08:43 AM »

it' past 120 days... just finished changing power and output transformers and some parts on an 807 amp....

Today will start on a new project... pictures soon...

ATJr. · « **Reply #44 on:** Nov 08, 2012 at 10:34 AM »

yan ba yung dadalhin nyo sa Ddusit?

stick · « **Reply #45 on:** Nov 09, 2012 at 07:17 AM »

^^ yup... will be finished today! most probably sunday ako punta...

ATJr. · « **Reply #46 on:** Nov 09, 2012 at 08:24 AM »

ingress starts at 4pm today...

stick · « **Reply #47 on:** Nov 21, 2012 at 08:38 PM »

Here is a Preamp I made... forgot when.... but it's a 5814 simple cathode follower... too lazy to finalize it... recent upgrades I made was to change the volume pot from 100k to 250k...

docrob · « **Reply #48 on:** Nov 21, 2012 at 11:27 PM »

nice one, james

stick · « **Reply #49 on:** Nov 22, 2012 at 07:18 AM »

Quote from: docrob on Nov 21, 2012 at 11:27 PM

nice one, james

Thanks Rob.... ikaw? gawa ka na din ng preamp!

docrob · « **Reply #50 on:** Nov 22, 2012 at 07:59 PM »

onga, need ko ng preamp to power my monos pero gusto ko me phono stage na rin MM/MC

basa-basa muna at tingin-tingin haha

stick · « **Reply #51 on:** Jan 31, 2013 at 10:05 PM »

At last, time to make a new amp!

stick · « **Reply #52 on:** Mar 16, 2013 at 08:02 PM »

Got a chance to make a push pull 6gv8, but apparently we didn't like the sound that much.. we then made an SE 6gv8 which sounded better..

I also made a PCB version of my cathode follower 12AU7. This gave me a hard time solving 60hz hum.. my point to point solder joint build is dead quiet.. I really wonder where this hum came from..

ATJr. · « **Reply #53 on:** Mar 17, 2013 at 08:47 AM »

you have to dc lift the heater to about 1/4 B+, a resistor voltage divider ought to do it....up to now i have resisted the urge to go dc on the heaters, a simple solution works best imho....

with tubes, less is more...

JojoD818 · « **Reply #54 on:** Mar 17, 2013 at 10:23 AM »

Quote from: TonyT on Mar 17, 2013 at 08:47 AM

you have to dc lift the heater to about 1/4 B+, a resistor voltage divider ought to do it....up to now i have resisted the urge to go dc on the haters, a simple solution works best imho....

you really hate them...

Quote

with tubes, less is more...

then stop using those CCS!

just making kulit on a beautiful Sunday morning...

ATJr. · « **Reply #55 on:** Mar 17, 2013 at 12:54 PM »

jojod, thanks for correcting my typo...fixed that...

there are reasons for using CCS, and we don't just stick them in.....but as you know, the common cathode is enough for almost all applications....

and as i said, if you don't know why your are using ccs, then don't....

i found out that with tubes, even the simplest of circuits can give you lots of listening pleasure...

stick · « **Reply #56 on:** Mar 17, 2013 at 04:36 PM »

Quote from: TonyT on Mar 17, 2013 at 08:47 AM

you have to dc lift the heater to about 1/4 B+, a resistor voltage divider ought to do it....up to now i have resisted the urge to go dc on the heaters, a simple solution works best imho....

with tubes, less is more...

already lifted the heaters, but the hum still remains... its really frustrating now... i have done a number of point to point soldered tube amps without HUM and I made an SE 6BM8 in PCB.. all without HUM... really makes me wonder why this 12AU7 preamp has HUM in PCB... I even made 2 PCB's with different trace routes but with the same result... maybe I should stick to point to point solder! hahaha...

ATJr. · « **Reply #57 on:** Mar 17, 2013 at 06:12 PM »

you can try the trick i told you about the last time i was in your shop....use 47k plate load in 1st stage and 47k cathode load of the follower, then adjust the cathode bias resistor of the 1st stage so that plate sits at 1/2 of B+.....

there is no shame in point to pint wiring if it does the job well.....

in the olden days, circuits used 20% tolerance resistors and they sounded good...

stick · « **Reply #58 on:** Mar 17, 2013 at 08:25 PM »

Will try this.. hopfully this would fix the problem.. by the way what would be the gain with this set up?

ATJr. · « **Reply #59 on:** Mar 17, 2013 at 08:58 PM »

Quote from: stick on Mar 17, 2013 at 08:25 PM

Will try this.. hopfully this would fix the problem.. by the way what would be the gain with this set up?

gain will be lower, if you are using cathode with capacitor bypass, gain will be higher...

gain is gm x rL, where gm is the transconductance at operating current and rL, this plate resistance in parallel with plate load resistor...

gm is cathode current dependent, and if any unbypassed resistor is in the cathode, this will be considered also...