36 watt (finshed) issues

[menger]

Heres a pix of my 36watt tmb not much done yet im still working on the board and found a issue withe the layout im using. i found a tmb layout in the gallery titled newlayout, on v2 theres a 1.5k resistor on pin 3 it does not show it grounded or attached to anything is this correct???? mark

[kedsinger]

It needs to be grounded. It's the bias/cathode resistor for that stage.

[menger]

Has any one built this amp with is layout? are there more errors on layout mark

[menger]

anouther one done i got it singing, but im getting some strange reading on the cathiod theres a 10v differance from powertubes4 v4 v5 and v6 and v7 all my other voltages seem in good range, im gonna up my cathiode resistor from one 125 to 150 im getting 9 volts on v4 and v5 and 22 volts on v6 and v7 and see where that gets me mark

[menger]

Ok i got the cathiods to 11.8 with a 150r, im gettig 326 on pin9 and 342 on pin7 and this is with 5ar4 so a 5y3 might get me in nice voltage range, sounds real sweet heres some pix cant wait till tommarow to open her up mark








r

[menger]

I got a chance to crank it up this morning, i realy like this amp anyone thinking a 18watt is not loud enough for gigging or jamming should try one of these, plenty loud, I do have few problems volume on(500ka) normal channel is not cutting off all the way??, and my feedback switch is not working, i used a on/off switch like i use on power and stand-by ?? mark

[menger]

Normal ch is not turning all the way off still getting volue with pot closed?? I dont beleave feedback is functioning properly what type of switch should it be? I had the cathiod bypass cap on v1 explode and shoot its insides all over my board on first fireup?? anyone seen this before???? Im getting 11.8 on pin 3 should i increase resistance a little to get it up around 12.5 or is this ok?? Im only using 5watt resistors on cathiod for power tubes should i up this to 10watters?? i dont know what i did but this is by far the quietest amp i've ever built, its dead silent wide open.. mark

[Shrapnel]

Mark,

some pots don't seem to zero-out, not a major deal really unless it bugs you or interferes with the sound. IMHO don't worry too much about it as long is it knocks the volume almost out completely.

[1950]

I printed that one out menger, my printout shows the 1k5 from pin 3-V2 earthed. I cant really help, but am interested in doing this one myself soon. Keep it posted please.

[rjgtr]

Normal ch is not turning all the way off still getting volue with pot closed??

Check the ground connection of the pot all the way to the chassis.

I dont beleave feedback is functioning properly what type of switch should it be?

Just about any switch will work. Check your connections in the feedback circuit.

I had the cathiod bypass cap on v1 explode and shoot its insides all over my board on first fireup?? anyone seen this before????

Yes. It was probably hooked up backwards. You need to be careful to get the polarity right on electrolytic caps.

Im getting 11.8 on pin 3 should i increase resistance a little to get it up around 12.5 or is this ok??

If it sounds good don't sweat it. Voltages have +-10-15 tollerance

Im only using 5watt resistors on cathiod for power tubes should i up this to 10watters??

5watt is enough.

[menger]

Eletrolytic was correct, it popped with a loud bang and shot its insides all over my tubes, i assume it was just a bad cap, the amp sounds great real gainy and smooth lots of bite just like a marshall should, its a keeper everyone should try one, The the pt i salveged from a old baldwin organ has a bit on a hum not real bad but a hum, may need replacement someday, it really is a woderful amp thanks mark