Dynaco 70 restore

[Eddie hy fi]

Looks good so far, I'd still replace the two 1.5 meg with 1.2 meg while you are in it.

Is there a easer way to do this mod , can i just put the 100 ohm resistor in line with the transformer wire going to term 4 , because other wise this mod is going to be way to much work , the transformer wire is not going to reach around to number 6 without a add on , yes the rest of mod is not to hard , should i just do a add on ? or a add a small terminal lug strip to fit the resistor in line

 

[Eddie hy fi]

im i going to need a Variac to start amp up for the very first try ?

 

[vintagetuber]

im i going to need a Variac to start amp up for the very first try ?

A dim bulb tester would be a better idea than a variac. Google it. Not too hard to make one, easier to buy one.

 

[Eddie hy fi]

ive now done the screen resistor protection mod , in my own way , hope its ok , the 100 ohm are one quarter watt , which sounds rite to act as fuses , stayed away from having to do anything to pin 6 ---------------------------------think im close to the end now , close to try out time

 

[Pio1980]

Is there a easer way to do this mod , can i just put the 100 ohm resistor in line with the transformer wire going to term 4 , because other wise this mod is going to be way to much work , the transformer wire is not going to reach around to number 6 without a add on , yes the rest of mod is not to hard , should i just do a add on ? or a add a small terminal lug strip to fit the resistor in line

Remember that the feedback wire to the board on one of each channel should attach to the tap side and not the tube screen side.

 

[Eddie hy fi]

Remember that the feedback wire to the board on one of each channel should attach to the tap side and not the tube screen side.

Yes i think i did that , only the quarter watt , 100 ohm , resistor is attached to number 4 now , i sprayed out the bias pots and the sockets , i think that im ready to set it up with all the tubes , but i do not have a variac to power it up ? so maybe ill just go for it , on hold for now , busy again helping others

 

[gadget73]

can always knock together a dim bulb tester. That will tell you if there are significant faults without letting the smoke out of anywhere.

 

[Eddie hy fi]

Well it does not work , after all that work and money , im in it for a grand now and i should have just bought a working unit ----it did come on and plays the right side only and well , but can not get sound from left , its not the input or pre amp , ive tried swapping tubes , same issue , then it blew a fuse when i was turning it off and on , and now its back up and going with same no sound issue on left , but with the brand new sovtek 5ar4 tube i get no sound at all , everything lites up but no sound , with the new JJ 5ar4 tube i do get the right side to play well , and when i put my ear to left speaker it sounds like amp is on but no sound there , what should i do ?

 

[Lavane]

The rectifier issue could be due to the sockets getting stretched out by the thicker JJ pins. You could try retentioning the socket. The Sovtek just may not be making good contact with one or more pins on the tube. You could retention the other tube sockets on the dead channel as well. Maybe take some good, clear pictures of the underside also. Maybe someone will notice something.
I've had problems in the past using JJ tubes. You can really have to use some pressure to seat them.

 

[Eddie hy fi]

The rectifier issue could be due to the sockets getting stretched out by the thicker JJ pins. You could try retentioning the socket. The Sovtek just may not be making good contact with one or more pins on the tube. You could retention the other tube sockets on the dead channel as well. Maybe take some good, clear pictures of the underside also. Maybe someone will notice something.
I've had problems in the past using JJ tubes. You can really have to use some pressure to seat them.

Ok thanks , not using jj output tubes there svetlana electron , a quad that i bought from a e-bay seller , only three of them seem to work , so i screwed up there too , but im using a xtra el34 tube that came with the amp and it seems to work and im able to set the bias on both sides

 

[Lavane]

Good to hear. Retentioning your power tube and rectifier socket is still a good idea, especially on an older amp. Try retentioning the rectifier socket and try the Sovtek again. Those JJ's do spread them out. I had to retention a power tube socket in my ST-70 because the JJ's I was using made one pretty sloppy and the heater in the tube in that socket wouldn't light up.

 

[Eddie hy fi]

Good to hear. Retentioning your power tube and rectifier socket is still a good idea, especially on an older amp. Try retentioning the rectifier socket and try the Sovtek again. Those JJ's do spread them out. I had to retention a power tube socket in my ST-70 because the JJ's I was using made one pretty sloppy and the heater in the tube in that socket wouldn't light up.

Dont really have the right tool to retention , i did just went over them a bit with a ice pick type tool but have not retested yet , im ok with the new jj rectify tube for now , to try and figure the dead channel issue , giving it a brake for now while i re think if i could have made some mistake or if there is a bad out put trany or what , im kinda stuck for now , while i recheck some things , --- wish i could trace the signal threw , but it just goes to the small tubes and im lost from there , test good to there on both sides --- im thinking thats its not a power supply issue as everything is lighting up and no smoke or smell and able to set bias and so on

 

[Eddie hy fi]

im now thinking tube socket issue , but on the PCB for a smaller tube input , in part because im using those adapters to convert to 6u8/ 6GH8A tubes -- the input signal seems to dead end there , for the left side , so maybe , not sure yet --wish i had some 7199 tubes to throw in to get around the adaptors , but i have none

 

[Eddie hy fi]

Well it does not seem to be a tube socket issue at all and all my wires and work seem ok , is there any way to check the left hand out put trany , i get no sound out of it on the 4 or the 8 ohm tap , but there is a faint background hum , if you put ear all the way up to speaker , like the amp is on with no signal , is there any way to trace sound signal to see if it makes it threw the PCB on the left channel ?

 

[gadget73]

where do you happen to be located? Possible someone could give you another set of eyes in person.

 

[kvflyer]

I don't have any suggestions about the signal loss in one channel without it being on my bench. Unfortunately, I would fail at "Phone Support" if I were a technician. Gotta have it in front of me, I have a problem with visualizing a problem.

But as for the fuse blowing, that can be caused by turning off any vacuum tube equipment and immediately turning it back on. It should always wait at least one minute for the filaments to cool down a little. Maybe that was the reason; maybe not.

 

[SS904]

is there any way to trace sound signal to see if it makes it threw the PCB on the left channel ?

The best way to trace an audio signal through an amp is to use a signal generator and an o scope. Inexpensive used scopes audio spectrum sig gens aren't break the bank purchases and pretty nice to have when working on this stuff.

 

[Eddie hy fi]

The best way to trace an audio signal through an amp is to use a signal generator and an o scope. Inexpensive used scopes audio spectrum sig gens aren't break the bank purchases and pretty nice to have when working on this stuff.

Not happening , the signal does not even get threw , no generator is going to push it threw ! wont spend another dime on this one , going to save up for a whole other amp or maybe replace the output trany in this one

 

[Eddie hy fi]

I don't have any suggestions about the signal loss in one channel without it being on my bench. Unfortunately, I would fail at "Phone Support" if I were a technician. Gotta have it in front of me, I have a problem with visualizing a problem.

But as for the fuse blowing, that can be caused by turning off any vacuum tube equipment and immediately turning it back on. It should always wait at least one minute for the filaments to cool down a little. Maybe that was the reason; maybe not.

yes i agree , the fuse was a old one that came with the amp , after putting a new three amp fuse in , that issue is solved anyway , now its just the dead channel , and i new i was taking a chance that the transformers where good , and they are probably not , maybe i can find one out put trans some how , some day , for now this whole project is a failure and i made to many bad choices and lost to much money on this , i kinda just want it out of my site and in the garbage

 

[SS904]

Not happening , the signal does not even get threw , no generator is going to push it threw ! wont spend another dime on this one , going to save up for a whole other amp or maybe replace the output trany in this one

Fair enough on the firmly held desire to not spend any more money. The idea of using a sig gen is to inject a known signal at the input. Using the schematic and a scope, you can then trace it through the audio path and see where it stops... Where it stops would be where you have a problem.