[RickH]

Hello,

I hope someone can help me.

I just got a 1962 Ampeg ReverbRocket, here is the schematic:


http://www.schematicheaven.com/ampeg...rocket_12r.pdf

I have two questions...

Looking at the tubes I noticed the former owner had plugged a 6SN7GT
into the PI circuit which calls for a 6SL7GT, I checked the TDSL site
and they do not list this as a substitute.

The amp sounds fine, but I was wondering if this is harmful and how the
amp performance will differ using 6SN7 instead of the called-for 6SL7?

The 6SN7 just appears to be a more robust tube 5W vs 1W plate and 450v
vs 300v. Does this mean it's probably ok to subtitute a 6SL7 with a
6SN7 but not vice-versa? Is the subbed 6SN7 now running a little
"starved" going into a 6SL7 socket? If so what is that effect on
performance/sound and is it harmful to other parts?

Also the Reverb is not working, to fix it I'm going to first replace
the reverb tube, assuming that does not fix it, I'll check basic
continuity on footswitch and tank connections. If that still does not
fix it, what would you check next? I have pretty good electronics
skills and basic test equipment. As you can see the reverb stage is
pretty simple.


thanks for your help,
Rick

[RickH]

Also amplification factor of 6SL7 is 70; 6SN7 is 20.

[RickH]

Thanks Patrick

I meant PI (Phase Inverter) which is V4 on this schematic. They left
V1 ok with the called for 6SL7. But substituted the phase inverter
with a 6SN7.

I dont get any boing with the reverb, when I get it disassembled I'l
check the coils. There is no reverb driver transformer.

Thanks
Rick


Patrick Turner wrote:
RickH wrote:

Hello,

I hope someone can help me.

I just got a 1962 Ampeg ReverbRocket, here is the schematic:

http://www.schematicheaven.com/ampeg...rocket_12r.pdf

I have two questions...

Looking at the tubes I noticed the former owner had plugged a 6SN7GT
into the PI circuit which calls for a 6SL7GT, I checked the TDSL site
and they do not list this as a substitute.

The amp sounds fine, but I was wondering if this is harmful and how the
amp performance will differ using 6SN7 instead of the called-for 6SL7?

The 6SN7 just appears to be a more robust tube 5W vs 1W plate and 450v
vs 300v. Does this mean it's probably ok to subtitute a 6SL7 with a
6SN7 but not vice-versa? Is the subbed 6SN7 now running a little
"starved" going into a 6SL7 socket? If so what is that effect on
performance/sound and is it harmful to other parts?

Also the Reverb is not working, to fix it I'm going to first replace
the reverb tube, assuming that does not fix it, I'll check basic
continuity on footswitch and tank connections. If that still does not
fix it, what would you check next? I have pretty good electronics
skills and basic test equipment. As you can see the reverb stage is
pretty simple.

thanks for your help,
Rick

I think you meant V1 instead of P1 mentioned above. Using a 6SN7 instead of
6SL7 anywhere
in the amp won't cause any overheating or damage.
But the 6SN7 has a voltage gain of about 15 compared to the 6SL7 with
voltage gain of about
35 or more, and tube sockets wired to take 6SL7 should only have 6SL7 used
if you like higher gain.

Make sure the spring box echo or reverb unit has continuity of both input
and output coils.
Is there an input transformer before the spring box? usually there is one
driven off the plate
circuit of the driver tubes, V3a in this case. V3b is the pick up circuit
at the other end of the springs,
and bumping the spring box with reverb in the circuit should produce boingy
sounds without any input signals.

Patrick Turner.

[Patrick Turner]

RickH wrote:

Thanks Patrick

I meant PI (Phase Inverter) which is V4 on this schematic. They left
V1 ok with the called for 6SL7. But substituted the phase inverter
with a 6SN7.

I dont get any boing with the reverb, when I get it disassembled I'l
check the coils. There is no reverb driver transformer.

I am not familiar with the reverb unit you have but most have a tranny drive to
efficiently excite the springs at one end with signal then a delicate pick up
coil at the
other to pick up the spring vibrations which simulate the echo of a tunnel etc.

The phase inverter could be 6SN7 because the common Rk is 1k, and loads are 47k.

It may also work with 6SL7 OK.

You should run a test signal, 400Hz, to the power amp input so there is
about 3Vrms output without distortion.
Then measure the grid signal input to each output tube.

Both grid drive signals should measure nearly equal, but opposite phase.
So grid to grid of the OP tubes should be twice each grid drive voltage.

The drive to the bottom 1/2 of the PI phase inverter is driven from 470k & 510k
divider,
with 470k&500pF from the join to 0V.
This looks more suited to the higher voltage gain of the 6SL7.

The dc voltages at the anodes of the 2 halves of the PI tube should be about
0.5 x the supply voltage.

The drive voltage equality can be trimmed by adjusting the value of the 510k to
being larger
or smaller, maybe with a temporary pot then replace with a fixed R when the pot R

is measured after getting the drive to be equal.


The 6SL7 used as a PI/driver will have more voltage gain than the 6SN7.
Your amp also has global NFB from the secondary of the OPT to the cathode of one
1/2 of the
PI/driver. So there is more NFB with the 6SL7 than if the 6SN7 is used.
Maybe you get a better sound with 6SN7.

Patrick Turner.



Thanks
Rick

Patrick Turner wrote:
RickH wrote:

Hello,

I hope someone can help me.

I just got a 1962 Ampeg ReverbRocket, here is the schematic:

http://www.schematicheaven.com/ampeg...rocket_12r.pdf

I have two questions...

Looking at the tubes I noticed the former owner had plugged a 6SN7GT
into the PI circuit which calls for a 6SL7GT, I checked the TDSL site
and they do not list this as a substitute.

The amp sounds fine, but I was wondering if this is harmful and how the
amp performance will differ using 6SN7 instead of the called-for 6SL7?

The 6SN7 just appears to be a more robust tube 5W vs 1W plate and 450v
vs 300v. Does this mean it's probably ok to subtitute a 6SL7 with a
6SN7 but not vice-versa? Is the subbed 6SN7 now running a little
"starved" going into a 6SL7 socket? If so what is that effect on
performance/sound and is it harmful to other parts?

Also the Reverb is not working, to fix it I'm going to first replace
the reverb tube, assuming that does not fix it, I'll check basic
continuity on footswitch and tank connections. If that still does not
fix it, what would you check next? I have pretty good electronics
skills and basic test equipment. As you can see the reverb stage is
pretty simple.

thanks for your help,
Rick

I think you meant V1 instead of P1 mentioned above. Using a 6SN7 instead of
6SL7 anywhere
in the amp won't cause any overheating or damage.
But the 6SN7 has a voltage gain of about 15 compared to the 6SL7 with
voltage gain of about
35 or more, and tube sockets wired to take 6SL7 should only have 6SL7 used
if you like higher gain.

Make sure the spring box echo or reverb unit has continuity of both input
and output coils.
Is there an input transformer before the spring box? usually there is one
driven off the plate
circuit of the driver tubes, V3a in this case. V3b is the pick up circuit
at the other end of the springs,
and bumping the spring box with reverb in the circuit should produce boingy
sounds without any input signals.

Patrick Turner.

[Patrick Turner]

RickH wrote:

I just noticed that the 0.5uF plate coupling capacitor going from V3A
to the reverb tank unit has its wax all melted off of it and dripped
down, most of the capacitor has no more wax at all. It's a paper/wax
tubular positioned on-end. Gravity and heat pulled all the wax down to
the bottom quarter of the cylinder. This appears to be the only
capacitor coupling anything in that reverb series, the recovery grid is
direct coupled, if the .5uF went open or shorted then there would
probably be no reverb or boing, so I'm going to check that one in
particular after I check the coils and mechanicals.

I'd replace all the old paper/wax caps with polyproylene or polyester rated at
630Vdc.
If the original 0.5uF was shorted, the coil in the tank would pull the anode
voltage to
nearly 0V.

Checking the dc anode voltage of the reverb tank driver triode would show
about +200V.

But coupling cap replacement throughout the amp is the first thing I would
recommend
if there are paper foil wax types there now.

Patrick Turner.



Patrick Turner wrote:
RickH wrote:

Hello,

I hope someone can help me.

I just got a 1962 Ampeg ReverbRocket, here is the schematic:

http://www.schematicheaven.com/ampeg...rocket_12r.pdf

I have two questions...

Looking at the tubes I noticed the former owner had plugged a 6SN7GT
into the PI circuit which calls for a 6SL7GT, I checked the TDSL site
and they do not list this as a substitute.

The amp sounds fine, but I was wondering if this is harmful and how the
amp performance will differ using 6SN7 instead of the called-for 6SL7?

The 6SN7 just appears to be a more robust tube 5W vs 1W plate and 450v
vs 300v. Does this mean it's probably ok to subtitute a 6SL7 with a
6SN7 but not vice-versa? Is the subbed 6SN7 now running a little
"starved" going into a 6SL7 socket? If so what is that effect on
performance/sound and is it harmful to other parts?

Also the Reverb is not working, to fix it I'm going to first replace
the reverb tube, assuming that does not fix it, I'll check basic
continuity on footswitch and tank connections. If that still does not
fix it, what would you check next? I have pretty good electronics
skills and basic test equipment. As you can see the reverb stage is
pretty simple.

thanks for your help,
Rick

I think you meant V1 instead of P1 mentioned above. Using a 6SN7 instead of
6SL7 anywhere
in the amp won't cause any overheating or damage.
But the 6SN7 has a voltage gain of about 15 compared to the 6SL7 with
voltage gain of about
35 or more, and tube sockets wired to take 6SL7 should only have 6SL7 used
if you like higher gain.

Make sure the spring box echo or reverb unit has continuity of both input
and output coils.
Is there an input transformer before the spring box? usually there is one
driven off the plate
circuit of the driver tubes, V3a in this case. V3b is the pick up circuit
at the other end of the springs,
and bumping the spring box with reverb in the circuit should produce boingy
sounds without any input signals.

Patrick Turner.

[RickH]

Patrick Turner wrote:

I'd replace all the old paper/wax caps with polyproylene or polyester rated at
630Vdc.

Patrick Turner.


Oops that would be all the caps in the amp, half are wax paper/foil,
the other half are plastic cased paper/foil. Nearly all of the caps in
the amp are paper/foil though, maybe one or two are ceramic. I cant
believe this amp idles so silently, no audible hum or hiss even with
the volume way up. There is evidence of some major overheating of that
..5 coupling cap to strip it's wax that completely.

[Patrick Turner]

RickH wrote:

Patrick Turner wrote:

I'd replace all the old paper/wax caps with polyproylene or polyester rated at
630Vdc.

Patrick Turner.


Oops that would be all the caps in the amp, half are wax paper/foil,
the other half are plastic cased paper/foil. Nearly all of the caps in
the amp are paper/foil though, maybe one or two are ceramic. I cant
believe this amp idles so silently, no audible hum or hiss even with
the volume way up. There is evidence of some major overheating of that
.5 coupling cap to strip it's wax that completely.

In any old radio of 50 years old the paper film caps are starting to fail,
often with disastrous consequences for the output audio tubes.
Amps are also prone to cap failure.

I always replace all the paper caps in old electronics.

Patricdk Turner.

[robert casey]

Oops that would be all the caps in the amp, half are wax paper/foil,
the other half are plastic cased paper/foil. Nearly all of the caps in
the amp are paper/foil though, maybe one or two are ceramic. I cant
believe this amp idles so silently, no audible hum or hiss even with
the volume way up.

All the more reason to recap, to preserve that amp. Before an old cap
gets leaky enough to mis-bias an output tube and burn out an output
transformer or such expensive hard to replace part. Use poly-something
caps for the replacements, like orange drops or such.

[RickH]

robert casey wrote:
Oops that would be all the caps in the amp, half are wax paper/foil,
the other half are plastic cased paper/foil. Nearly all of the caps in
the amp are paper/foil though, maybe one or two are ceramic. I cant
believe this amp idles so silently, no audible hum or hiss even with
the volume way up.

All the more reason to recap, to preserve that amp. Before an old cap
gets leaky enough to mis-bias an output tube and burn out an output
transformer or such expensive hard to replace part. Use poly-something
caps for the replacements, like orange drops or such.

Thanks, now I have a good reason to buy that de-soldering vacuum I told
myself I would need one day.

[Ned Carlson]

RickH wrote:

I just noticed that the 0.5uF plate coupling capacitor going from V3A
to the reverb tank unit has its wax all melted off of it and dripped
down, most of the capacitor has no more wax at all. It's a paper/wax
tubular positioned on-end. Gravity and heat pulled all the wax down to
the bottom quarter of the cylinder. This appears to be the only
capacitor coupling anything in that reverb series, the recovery grid is
direct coupled, if the .5uF went open or shorted then there would
probably be no reverb or boing,

Actually, even if the reverb *driver* doesn't work, you'll
still get the boing if the other end of the circuit (recovery)
still works and all the connections and coils are OK.

I'd start by swapping or checking continuity on the RCA
cables (the originals were cheap), cleaning the reverb
input/output jack (again, cheap and easily corroded,
bad connections can kill the small signal)
and checking voltages on the recovery end.

Ampeg tanks are direct drive (no reverb transformer),
the DC ohms should be fairly high on both ends, like
in the hundreds of ohms. If it's way too low one one
end the coil is shorted or someone tried subbing a Fender
tank (which has an 8 ohm input).


--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net

[RickH]

Ned Carlson wrote:
RickH wrote:

I just noticed that the 0.5uF plate coupling capacitor going from V3A
to the reverb tank unit has its wax all melted off of it and dripped
down, most of the capacitor has no more wax at all. It's a paper/wax
tubular positioned on-end. Gravity and heat pulled all the wax down to
the bottom quarter of the cylinder. This appears to be the only
capacitor coupling anything in that reverb series, the recovery grid is
direct coupled, if the .5uF went open or shorted then there would
probably be no reverb or boing,

Actually, even if the reverb *driver* doesn't work, you'll
still get the boing if the other end of the circuit (recovery)
still works and all the connections and coils are OK.

I'd start by swapping or checking continuity on the RCA
cables (the originals were cheap), cleaning the reverb
input/output jack (again, cheap and easily corroded,
bad connections can kill the small signal)
and checking voltages on the recovery end.

Ampeg tanks are direct drive (no reverb transformer),
the DC ohms should be fairly high on both ends, like
in the hundreds of ohms. If it's way too low one one
end the coil is shorted or someone tried subbing a Fender
tank (which has an 8 ohm input).


--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net

Ned,

I'ts the original tank, and I was wondering what general impedance to
expect, I know the Fender tank input is basically just like a speaker
voice coil.

I am In the Mokena/Frankfort area, do you have a tube or amp business
on the SW side of Chicago?

I grew up on 60th & Tripp, and am always looking for local businesses
to support my hobby.

Thanks

[RickH]

Ned Carlson wrote:

Ampeg tanks are direct drive (no reverb transformer),
the DC ohms should be fairly high on both ends, like
in the hundreds of ohms. If it's way too low one one
end the coil is shorted or someone tried subbing a Fender
tank (which has an 8 ohm input).


--
Ned Carlson
SW side of Chicago, USA
www.tubezone.net

I got 180 ohms on the input side and 178 ohms on the output side.