All non-insulated transistors should be insulated with a mica or sil pad and an isolation washer .... You can get away without one if there is no way the heatsink will come in contact with ground ......

Quote from: Farthing on December 03, 2011, 06:22:54 AM

Can someone advise on  the correct way to solder the kind of voltage regulators found in amps ? ie; TDA 2050. Some suggest earthing the body to ground and then there is the question of the correct soldering iron temp.

You don"t want to tie the body of a voltage regulator to ground , the Body usually carries the output voltage on it so tieing it to ground will destroy the regulator and cause some sparks and even do other dammage ......
If the regulator needs to be heatsinked to the chassis then you should isolate the chip from the heatsink useing a sil/mica pad and an isolation washer for the mounting bolt and test that there is no continuity between the chip body and the chassis .......

Most all transistors , power amp IC"s and regulators need to be isolated from ground unless the IC has a plastic package .....

Quote from: phatt on October 19, 2011, 09:07:25 AM
Hi Minion,
             Mate,, great effort :tu: Just looked at the pics. Wow a lot of work in that one so glad you got it all working.
Forgot the ground ay?  Yep been there a few times.
The ground is always the wire you forget to add :grr

One little thing,,, if I may be allowed?
Do I see Wires passing through holes with no grommets and around sharp metal edges?
can be an issue down the track. :trouble

Cheers, Phil.

Thanx for the tip about the holes , there is enough slack on the wires so they hopefully it won"t be rubbing , I also don"t put it on top of my speaker cab because I don"t want to abuse it .... I will put some silicone glue around the holes to stop any rubbing .....

The amp has a sort of old school metal tone but It is hard to get the Clean channel to stay clean and be loud so I"m gona replace the two 12ax7 in the Clean channel with some 12au7 or 12at7 to get a cleaner tone ...... Using the Sonic Maximizer and EQ in the FX loop helps shape the tone quite a bit and makes it a bit more versitile .....

And the chanell switching curcuit works flawlessly , I made the footswitch out of a plastic project enclosure and a heavey duty push button switch and a 1/4 in female jack , it connects to the amp with a regular patch cord .......

It is by far the hardest project I have done which was componded by my total ignorance in Tube theory and my pathetic and dyslexic math skills .......

I will eventually post the PCB artwork , stuffing guide and wiring diagram I just haven"t had the time to finnish the stuffing guide .....

Cheers

hi , I did it that way because it was just a lot easier to wire up with the pots in that position ..... yes the front plate is aluminium , I got 3 of them at the local metal supermarket for about $12 ......
The rest of the chassis is from a old EQ I found in a junk pile .....

I"m going to redo the magic marker labeling at some point because it takes away from the amps awesomeness ....

I also used some aluminum plate between the Power Transformers and the audio curcuits to shield some of the EM from the power transformers ....

You can"t see them in the picture but there are 3 seperate power transformers , I have a 235v transformer for the Plate supply that has a 6.3v tap that is unused and a 5v tap used for the Relay channel switching , it also has a seperate 12.6v 1A transformer for the Heaters and a seperate 100Va 2 x 18v transformer to run the LM3886 , there is also a 100mA 10H Choke .......
It was a lot of work trying to find away to fit all that stuff inside that Chassis ......

I"m now working on a 6V6 Power amp that I can use with the Line out on this amp to get that pentode tone ..... It"s allready built for the most part , just have to wire it up and find a chassis for it and hope it doesn"t catch fire ......

Cheers

Here are a couple Pics of them amp .....

If you put a resistor of say 100k in paralell with each filter cap in the PSU it will help even out the Voltage on the Positive and negitive rails and give you a more stable Ground .....

Well ,if even the lights don"t come on when powered up and the fuse is good then it to me seems that it could be a bad power transformer .....

Success !!! Ive been stumpted by this really bad hum problem so after a week of thinking on it I realized that I forgot to ground the circuit that runs the channel switching circuit ...
The channel switching circuit uses 2 5v relays to switch the 2 channels and the led indicator lites for each channel and runs off of a 6vac winding of one of the transformers that powers the tubes , it uses a footswitch that connects to the amp via a patch cord .....
After grounding the 6v winding the hum totally dissapears , sounds great and it loud as hell ....

I actually built this amp because the other amp I built died , but I come to realize tonight that it didn"t die at all , it was the 15 band EQ I bought that I used in the FX loop that died ....

go figure , you build an amp and it last longer than the store bought EQ that you bought to use with it ...... 

Im running my Preamp into a LM3886 with an input impedance of 47k , I have a solid state buffer but I"m not using it because I tried it with the buffer and it really didn"t sound any different accept it was louder with the buffer but It is plenty loud enough allready , so loud that it clips the lm3886 with the Volume barely on ..... 

The circuit will be buffered anyways because I usually have my EQ and a couple pedals running through the FX loop ......

Thanx

Even with the tone stack at the end of the circuit the signal is still very very hot ......

This is a schematic of my new tube preamp ..... it"s very high gain and sounds great ... it is simular to most designs but also a bit different .....

I also have a PCB design for this preamp that I will post after I get the build instructions finnished ....

Cheers

I just realized I mis-spoke in my post .... Channel 1 has 47uF local filtering and channel 2 has 22uF ..... Both channels have the exact same grounding scheme but I suppose it could be just wires laying in the wrong place , I"ll work on that ....

I"ll post pics once it is done , or at least mostly done .....


Cheers

Well guys , I finnished designing and building my Relay board , after a coulpe false starts (I screwed up the PCB so I had to cut a couple traces and run jumpers) I got it working perfectly .... It makes no noise switching and the proper LED lights to indicate the channel selected ......

I got the PCB down to about 2.15in x 2.15in , but even then i had a hard time finding a place in the Chassis to mount it and ended up mounting it above the power amp ......

The Chassis is only 6in high , 6in deep and 16in long and it has 2 preamps (4 tubes) , the High voltage Power supply (200uF at 400V) the high Voltage transformer , a 10H choke , a 1A 12v Transformer for the heaters , a stereo TDA7293 with speaker protection and a 400Va Transformer , the Relay switching circuit and the solid state buffer .....
Needless to say it is a very cramped chassis , I also used aluminum plate to seperate the power transformers from the audio preamps to offer some protection from the EM from the transformers ...... I just have to hook up the Power amp now .....

I do have one problem though , Channel 1 sounds great and its totally noise and hum free , But Channel 2 which also sounds great , has quite a bit of hum , both channels are identical accept the one that hums has 22uF of local supply filtering and the one that hums has 22uF ...... Could this be causing it to hum ?? or be why the good channel doesn"t hum ??


Thanx

Quote@Minion,
          I'll soon be posting my updated floor preamp circuit that might give you some ideas to work with.
Phil.

I look forward to it ..... I"ll eventually get around to posting a Zip file of PCB and Layout/Schematic for the Tube preamp , I don"t want to post the PCB images because it is from a PCB I bought on-line that I converted to a single sided version and changed some Values in .... I don"t know what the protocal is for basterdized versions of someone elses design ......

Thanx guys ....

Hi < Thanx .... I was going to do a PCB for the Realy as I do PCB"s for allmost everything even with LED"s which I am also going to add to show which channel is being used....... I have (2x)24v AC(34vDC) available and two 6-8v AC rails that I"m not useing and a 320v DC rail that I"m useing for the tubes in the preamp and a 12v AC rail that I"m useing for the heaters but it is useless for anything other than heaters as it is elevated to 30v and not referanced to 0v .....

Maybe I"ll use the 6-8v AC rail and use 5v relays because they aren"t being used and they have 0.5a and 2a current capabilities ......

If is a 2 channel tube preamp with tone controlls and solidstate buffer on the output of the preamps and into a stereo TDA7293 poweramp  and an effects loop for my 15 band EQ .......

Thanx