Back with a nagging question

turnitdown

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I have been gone for a bit...life events. All is good now and I got a grandson in the bargain.

I had an amp, that I sold, that was unique in that it was a single-ended 6BQ5 with no preamp tubes. My SS preamp, or anything else that could produce enough voltage went directly into pin 2. Again, no preamp tubes.

Was this possible? Did it need at least a cap between the jack and the tube?

If this is possible, can on do this into the phase inverter of a PP amp?

The reason I ask is, I prefer all the settings, selections and remote control of of the SS preamps.
 
The driver was definitely in the SS preamp (an Adcom) but the input jacks on the 6BQ5 amp went directly to the grids.
 
Thanks, I'm right there with your train of thought. To get full output it would take more input voltage and everything running correctly downstream from there.
 
Without having it here anymore, that's hard to say whether it did or didn't. Judging how well it played with the preamp, I'm going to say there was a grid leak resistor in there.
 
If I can find a pic, have a look at some of the RCA tube amps. There is one RCA power amp from a console that only has the power transformer, can capacitor, two 6BQ5 tubes, and two output transformers.

All the preamp action along with a 12AX7 or 6CG7 type of tube, was being done on the preamp / tuner chassis of the console.

Can't remember his name so maybe he will see this thread and chime in, but a member here added an extra tube to one of his RCA amps from a console that didn't have enough gain.
 
That would be great. I have quite a few parts laying around in the garage. They need to be assembled, amp and speakers - so, any schematic for that floating around would be great.
 
The coupling cap was probably on the preamp side, also. It's a bit unusual to find a split chassis like that but it's not a problem to have the jack wired to the grid. That's the way most inputs are. Some have a cap after the jack but it's not required unless you need to block a DC voltage that may be on the signal line. Your preamp probably supplied a couple of volts of signal which will make a good bit of volume but it wouldn't get up the @7v of what is normaly full drive to a SE 6BQ5.
Many of the vintage single ended console amps had just the output tube section on a separate chassis which was usually connected via an umbilical cord. The power supply also was located on this chassis. This makes good sense haviing the AC and power supply away from the very sensitive preamp and tuner sections.
 
Nice job. That's one of them, the RS 203 is another. I've got the pieces to build that. I'll go looking for a schematic. Easier to copy.
 
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Nice job. That's one of them, the RS 203 is another. I've got the pieces to build that. I'll go looking for a schematic. Easier to copy.
I rebuilt 2 of those the same way using the RH84 circuit. I made it so that output from each amp could be paralleled so as to double the power and one could use 1 amp per channel. Or flip the switch and you go back to a stereo amp. The rh84 circuit is an excellent sounding one for the console single ended amp.
 
The other problem with designs like this, you can't easily implement global negative feedback unless you're willing to add a return cable from the amp and have the preamp modified suitably to make it all tie together. Personally not a fan of split amplifiers for that very reason.
 
Very true. Thanks. I'll add a pre stage on the chassis and call it a day.; I just want to button up a few unfinished projects to clear some space.
 
Very true. Thanks. I'll add a pre stage on the chassis and call it a day.; I just want to button up a few unfinished projects to clear some space.
If your unit is like the amp shown in post #15, there are 3 9 pin tube sockets. And i believe that this amp is SS rectified. so, that should leave the solo socket for the driver tube and the paired sockets for the el84s. I am not sure if the original chassis is wired this way or if i had to gut it and make it so. Either way it is not that hard dealing with just gutting and rewiring 3 sockets. The RH84 circuit is very simple, which is part of the reason for its good sound and popularity.
 
That's the amp! It only has two 9 pin sockets. The smaller one to the right appears to be an umbilical (4 or 5 prong).
Ok. if that solo socket is actually a connector for the umbilical then one would have to remove the socket and using a step drill increase the size of the opening large enough to put a noval socket in it. It is quite easy to drill out even a steel chassis. Then put your 9 pin socket upside down in the hole after checking how you want to position the socket so as to more easily array all the caps and resistors that will attach to it. Mark the mounting screw holes, drill those out and remount your socket. Easy peasy. I wish i had kept pictures of that build just to have a record.
 
Ok. if that solo socket is actually a connector for the umbilical then one would have to remove the socket and using a step drill increase the size of the opening large enough to put a noval socket in it. It is quite easy to drill out even a steel chassis. Then put your 9 pin socket upside down in the hole after checking how you want to position the socket so as to more easily array all the caps and resistors that will attach to it. Mark the mounting screw holes, drill those out and remount your socket. Easy peasy. I wish i had kept pictures of that build just to have a record.

Piece of cake. Thanks. I have the tools, tech and, "some", know-how...I think. I'm not crazy about the old chassis so I'll be pulling the parts to build it in a cigar box (wooden). I've collected some empties the liquor store gives away when I go in for wine.
 
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