Can anyone tell me why the symptoms of
using a wrong rectifier tube in a music instrument amplifier?
The amp would be a Fender Super Reverb 2* 6L6, 6 * 12AX7s.

For example, if the amp calls for a 5U4G or 5AR4
and a 5V4 is installed in this amp,
what would the symptoms be?

Could they be voltages fluctuations (to lower voltages).
Sound fluctuations (to amp be coming quieter when played).

There are a lot of rectifier tubes (and virtual tubes) out there and
there are several things to consider.

Assuming that it even has the same base as the designed-for tube (else
it would not plug in), is its pinout the same? Most octal base
rectifiers share a common pinout, but depending on the circuit, the
small differences may cause problems.

The heater draw is important because a heater that pulls too much
current can overstress a marginal heater winding. This is a separate
winding, at 5 volts, from the 6.3 volt one for the other tubes.

The voltage drop, or lack thereof, may cause problems. Use of mercury
vapor or xenon rectifier tubes in place of vacuum types, or solid state
diodes if appropriate dropping resistors aren't added, can cause
voltages higher than power tubes and filter capacitors are rated for.

Guitar amps are today almost operated "outside design spec" anyway-Leo
never intended them for sustained operation with everything on 10!
People swap rectifier and output tube types all the time for changes in
the distortion and compression produced, and it's pretty well
established what is and is not OK for most amps. If you blow a
transformer, that's OK with most players-put in another one, unless
it's a particularly oddball or expensive amplifier.

Spike wrote:
Can anyone tell me why the symptoms of
using a wrong rectifier tube in a music instrument amplifier?
The amp would be a Fender Super Reverb 2* 6L6, 6 * 12AX7s.

For example, if the amp calls for a 5U4G or 5AR4
and a 5V4 is installed in this amp,
what would the symptoms be?

Both 5AR4 & 5V4 will provide slightly higher dynamic-condition B+
voltages with less droop so will give a firmer bottom end than 5U4.
Both will also reduce PT load by 5 watts permitting it to run very
slightly cooler. 5AR4 has controlled warmup, which is unimportant in a
SR which has a STBY switch in use. 5AR4 may have shorter service life
because it does not like to be hotswitched (Stby switch) but tolerates
it in a SR. Best overall operation will be by SS rectifier sub.

what if you use a 5AS4

"Spike" wrote in message
...
Can anyone tell me why the symptoms of
using a wrong rectifier tube in a music instrument amplifier?
The amp would be a Fender Super Reverb 2* 6L6, 6 * 12AX7s.

For example, if the amp calls for a 5U4G or 5AR4
and a 5V4 is installed in this amp,
what would the symptoms be?

Could they be voltages fluctuations (to lower voltages).
Sound fluctuations (to amp be coming quieter when played).

Generally speaking, nothing can be said. In the low range, 5V4 and 5AR4 do
not differ very much, but the 5AR4 is much beefier. 5U4 is completely
different: a big tube, with large power handling capability, but having a
higher voltage drop. Many things can happen:
- if You place a much smaller tube in (ie. a 5Y3 instead of a 5R4WGB) You
can fry it in a few days, while getting in the meantime a lower B+ - less
power and earlier distortion
- if You swap an indirecly heated tube with a directy heated one (ie. a
5AR4 with a 5U4G) You'll probably get a B+ surge at power-up and blow some
cap
- if You plug a larger tube in (ie. a 5U4 instead of a 5Y3) You're just
wasting filament heating watts to get about the same B+
Briefly: leave it as specified unless You have a PS schematic and You have
already re-calculated it all with Duncan's PSU software for the new
conditions

Ciao

Fabio


"Spike" ha scritto nel messaggio
...
Can anyone tell me why the symptoms of
using a wrong rectifier tube in a music instrument amplifier?
The amp would be a Fender Super Reverb 2* 6L6, 6 * 12AX7s.

For example, if the amp calls for a 5U4G or 5AR4
and a 5V4 is installed in this amp,
what would the symptoms be?

Could they be voltages fluctuations (to lower voltages).
Sound fluctuations (to amp be coming quieter when played).

Fabio Berutti wrote:
(snip)
- if You swap an indirecly heated tube with a directy heated one (ie. a
5AR4 with a 5U4G) You'll probably get a B+ surge at power-up and blow some
cap.

No caps blown. Actually just the opposite happens. B+ rises with a 5AR4
compared to 5U4G about 20 - 40v.


Fabio,

Thanks. And thanks to everyone else also.

Regards,

Spike