[getllamasfast]

Quote:

Originally Posted by the_equalizer /img/forum/go_quote.gif Beautiful pics my friend ! Nice to see another 12AU7 build So, did you solve the noise issue you were having? cheers!

Thank you!

Yeah, I did fix it, although I'm not exactly sure how...

I just put it together one last time and it suddenly just worked!

Nice job on the 12AE6 amp!

 

[ezzieyguywuf]

Haven't been up here in a while, but I been itchin' to build one of these. I still can't seem to locate these tubes though. Tubedepot has them for 15 bucks a pop, but I'm wondering if you guys could suggest anywhere else I could purchase them more reasonably. I truly am a starving student, soon to be starving newly-wed! lol

 

[tomb]

Quote:

Originally Posted by ezzieyguywuf /img/forum/go_quote.gif Haven't been up here in a while, but I been itchin' to build one of these. I still can't seem to locate these tubes though. Tubedepot has them for 15 bucks a pop, but I'm wondering if you guys could suggest anywhere else I could purchase them more reasonably. I truly am a starving student, soon to be starving newly-wed! lol

Last time I looked, SND Tube Sales (vacuumtubes.com) had them for $10.

 

[simwells]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Last time I looked, SND Tube Sales (vacuumtubes.com) had them for $10.

When I was looking SND didn't have any left, but Radio Tube Supply had some at $10

 

[the_equalizer]

Quote:

Originally Posted by iPoodz /img/forum/go_quote.gif Excellent work, equalizer! I don't understand all the details, but it's great that you are able to adapt the amp to whatever parts are available to you. I jumped on the kit because I don't think I'd be able to do that getllamasfast, what case are you using? Did you get the holes precut?

Quote:

Originally Posted by getllamasfast /img/forum/go_quote.gif Thank you! Yeah, I did fix it, although I'm not exactly sure how... I just put it together one last time and it suddenly just worked! Nice job on the 12AE6 amp!

Thanks guys! I just tried to work out another option to build this amp despite the growing scarcity of the original 19J6 tubes; 12AE6 can be found easily and for at least half of what 19J6's or 12AU7's cost.

Also, checkout the power supply in ebay. You can get one for $6.00 to $9.00 USD

I've been listening to the prototype on and off since yesterday and it really sounds well. For one, even though it's wired in a protoboard, it's very very silent: I'm listening to a CD edition of a 1963 recording, and above the amp's noise floor, you can clearly hear the tape hiss when the music starts.

About the bias current I browsed the MiniMAX website and it turns out the current I got in my prototype is very similar to what they chose for the quiescent current of the tubes in the MiniMAX. The problem lies in the fact that they recommend 13.5 volts and upwards for the tube plates and I'm running them at 10! I trust that tomorrow I can go by the electronics store and pickup some resistors to try as plate loads and push the plate voltage up to around 15 volts. That should improve the sound quality.

So, there it is, another option if you guys want to build this fun little amp.

cheers!

 

[Narwhalius]

Hey all,

Still having issues with no sound on my left channel. Got myself a multimeter but I really have no clue on how to use it. Followed the directions that came with it to test for continuity. Touched the backside of each RCA jack, not the wire but the part where you screw on the screw to tighten it to the panel, to the R spot on the block. The meter moved a little bit. Tried the same thing with the L spot and the meter never moved. Are those correct spots to test at? Anywhere else I should be testing?

 

[timmyGCSE]

I was all ready to go ordering parts for a mini3 this morning but the US$ - GB£ exchange rate is poor meaning the PCB etc. from AMB was more expensive, £57 there or thereabouts in total.
So I thought hmm price up a SSHA 12AU7 version..
components, cisco PSU from ebay, Philips 5963 NOS tubes and tube holders £46.10 all in, about a tenner less. I was going to use the mini3 for desktop use anyway so I went for the SSHA instead

next jobs are to relearn to read schematics after doing electronics in college and find/make a suitable case for all the biz.

can't wait

edit: oh and if anyone needs some resistors for this build I will have plenty! Rapid electronics sold them in packs of 100 for 50p each! haha

 

[Entropy1]

I've done some more testing and the heaters on both tubes are getting the proper 20v. I don't understand how each channel on the amp has exactly the same resistances but produce different volumes along with the channel bleed. Sorry to keep posting but I really want to get this working.

 

[the_equalizer]

Quote:

Originally Posted by timmyGCSE /img/forum/go_quote.gif I was all ready to go ordering parts for a mini3 this morning but the US$ - GB£ exchange rate is poor meaning the PCB etc. from AMB was more expensive, £57 there or thereabouts in total. So I thought hmm price up a SSHA 12AU7 version.. components, cisco PSU from ebay, Philips 5963 NOS tubes and tube holders £46.10 all in, about a tenner less. I was going to use the mini3 for desktop use anyway so I went for the SSHA instead next jobs are to relearn to read schematics after doing electronics in college and find/make a suitable case for all the biz. can't wait edit: oh and if anyone needs some resistors for this build I will have plenty! Rapid electronics sold them in packs of 100 for 50p each! haha

Cool! another 12AU7 build in the making! Please post your progress/impressions !

Quote:

Originally Posted by Entropy1 /img/forum/go_quote.gif I've done some more testing and the heaters on both tubes are getting the proper 20v. I don't understand how each channel on the amp has exactly the same resistances but produce different volumes along with the channel bleed. Sorry to keep posting but I really want to get this working.

As TomB posted before, those problems MUST come from a miswiring of some kind, as the PCB is a proven build. Clear pics would help us help you.

What you describe as "channel bleed" seems particularly strange. What is your source ? Have you tried different sources ?

The lower volume in one channel, if not caused by the tube (easily checked by swapping the tubes) can be caused by cold solder joints, incorrect value resistors, or a semi-fried MOSFET; you should check the solder joints of your headphone jack too.

cheers!

 

[Juaquin]

Have you tried playing an audio track that plays only one channel at a time, to confirm this channel bleed? There is a Left Right track on this page, along with a bunch of other fun test tracks.

As for mismatched volume, there are a number of potential causes. The volume pot is not tracking well (especially in the low levels), you have bad joints or connections in one (or both) channels that are adding resistance, or the tubes (although I doubt this since TomB is very good about matching them for the kits).

 

[Entropy1]

Thanks for the response equilizer. Yes, the channel bleed is what bother me most also. I've tried different sources along with different rca cables. All of what I test does fine in other systems. I know there is channel bleed because I can disconnect either RCA jack completely, and still hear things in both channels. I can't think of anything other than a bridge causing this problem but I don't know. Perhaps a few more alcohol baths for flux?

I have also swapped tubes to try and determine which tube was at fault, if either. When doing this I get the same result suggesting both are good and not the cause of the problem. I have also swapped to a new set of MOSFETs with no change. The headphone jack looks to be soldered in well but I will go over it again just to make sure.

 

[UKToecutter]

Post some nice close up pictures of your RCA wiring and the underside of the board

 

[timmyGCSE]

Quote:

Originally Posted by the_equalizer /img/forum/go_quote.gif Cool! another 12AU7 build in the making! Please post your progress/impressions !

yep shall do, still fretting over the case, I want to make it look nice as well as sound good

I was pretty pleased with the tube find, £5.50 ($8.50) each, ECC82/12AU7 equivelent, this is a few notes I've found on them:

Quote:

very close to ECC802S 5963 Special Quality ECC82: Different in two points: 1)Longer Stand by function 2) balanced tube by default. * With those two points you have basically the same properties as the Telefunken ECC802S. These are the pearls

Quote:

This is a nice industrial type which is nearly identical to the standard 12AU7. RCA made a nice blackplate version of this tube, Sylvania has a gold pin version, and GE has it in their 5-star broadcast line. The plate voltage rating is a little lower than for a 12AU7, but for most applications, it will work fine. It has a rugged cathode and should be long lived, similar to the 5814. Watch this tube, as it is plentiful now and prices are low. As audiophiles discover it, the rush will be on!

still going on ebay uk:
5963 PHILIPS ECG 12AU7 ECC82 TUBE VALVE 1 PC on eBay (end time 09-Mar-10 12:47:43 GMT)

 

[Entropy1]

When testing for the channel bleed, I noticed that in one channel, I get the same volume regardless of where the volume pot is. To me, this would suggest that there is a problem before even hitting the volume pot, yet I can't seem to find any bad connections. Are there any other inferences I'm missing? How often are volume pots bad? I'm sure it's more likely that I messed something up rather than a component being bad, but I've gone over it so much. Anyways, thanks again and I'll keep looking.

 

[UKToecutter]

The volume pot is the first thing the signal hits after the input resistors (R16/R17)