Fender Pro Reverb

[caveing]

I have a Pro reverb- and while I've loved it for many years my current situation is deeming it to not have enough headroom. When I first got the amp it just had a ridiculous amount of headroom- but it was colder and more sterile sounding- right now it sounds pretty dang good. It breaks up around 5-6 on the dial- well it begins getting hairy there. It used to be too loud to bear at 5 and super clean. I feel like its supposed to sound like it does now anyways, so moving on...

Today I played a Fender Pro tube Twin- a newer model twin that has a dirt channel and fx loop and all that jazz- but it also had a 25/100 lo/hi switch. I loved the sound out of this amp- it was fat and punchy- just generally bigger sounding than my amp. My pro reverb has a weber california (which is supposedly a big sounding JBL type speaker)... I'm thinking the problem is the smaller transformers of the pro reverb as well as the fact that it's an early silverface pro that utilizes a 5u4 rectifier instead of the blackface that uses a GZ34. I've tried a gz34 but I feel like it increases the plate voltage too much and makes the amp sound different- in a way that I dont like. The pure cleans are fine with the GZ34- but when it starts breaking up- it doesnt sound nearly as good as with the 5u4.

So I was thinking of putting larger transformers in the amp like Super Reverb Sized. My questions are- Should I replace both power and output... I know replacing the power transformer I would have lower voltages and be able to use a GZ34 or SS rectifier to get that punchy twin sound. BUt the output transformer is more responsible for punch and headroom right? About how much more headroom would I get from increasing either or both of these? I wish I had the money or resources to just experiment, but I dont.

I've also heard of 7581 power tubes being a good way to increase headroom- about how much would those increase versus transformers?

Should I just sell and go with a twin?

The thing is that I like the 2 power tube setup. A twin i feel has to be SUPER loud before it starts hitting its sweet spot. I feel the 2 power tube pro will have its sweet spot at a more manageable volume, well I know it does, but with larger transformers I'm wondering if I'll get that punchy clean fat twin sound at a bit lower volume?

I really dont like super reverbs- but I think it's just that I dont like 10's. I really liked a bassman 50 I played with 2 eminence red white blues...

Anyone have good priced recommendations for a transformer or transformers?

[Firestorm]

So I was thinking of putting larger transformers in the amp like Super Reverb Sized. My questions are- Should I replace both power and output... I know replacing the power transformer I would have lower voltages and be able to use a GZ34 or SS rectifier to get that punchy twin sound.

I don't know what you mean by "larger" transformers.

On paper, the power transformer used in the Super Reverb is the SAME one used in the Pro Reverb (and the Bandmaster Reverb and later Vibroverb amps). Although the part numbers didn't change, later versions of this PT were speced for higher secondary voltages to allow the use of the cheaper 5U4 rectifier. So maybe what you need is a "smaller" transformer (in terms of secondary voltage). A Hammond 290DX (replacement for Fender part 125P5D/022798) shows secondaries of 325-0-325, so lower than the 375-0-375 shown on the AA270 Pro Reverb schematic.

As you said, breakup sounds better to you with the 5U4, but you want it punchier. A 5U4 is anything but punchy, but drops your plate voltages compared to a 5AR4. So lower voltage secondary may be the way to go.

This is the same amp you've talked about in other threads, right? It used to sound one way and now is different. Did we ever establish how your bias was set then versus now? In order to sound like Fenders, Fender amps are biased more towards the Class B side of Class AB (a little over 50% of max dissipation) rather than towards the Class A side (the 70% that guys like Aikens recommend). Nothing wrong with 70% per se, but it won't sound like a Fender and it's kind of a waste of output power (more heat instead of more sound).

[Super_Reverb]

that it's an early silverface pro that utilizes a 5u4 rectifier instead of the blackface that uses a GZ34. I've tried a gz34 but I feel like it increases the plate voltage too much and makes the amp sound different

Headroom is about having sufficient voltage on your power supplies so that the signal does not clip or swing too close to rails to become extremely non-linear. A clean amp needs sufficient voltage so that the signal can swing through every stage in pre, PI, and power stage without extreme non-linearity. This means choosing your PS voltages and bias points (Rk and Rp) so that the plate bias voltages are mid supply or a scosh above mid point.

Transformer flux saturation and speaker characteristics also play into this.

So using a rectifier that yields higher plate voltage should push you to higher headroom.

If you haven't swapped tubes or made any adjustments, then you have a component failure or you are simply seeing effects of ageing components.

Suggest you check PS, plate and cathode bias voltages to see if the amp is still properly setup.


rob

[caveing]

So I was thinking of putting larger transformers in the amp like Super Reverb Sized. My questions are- Should I replace both power and output... I know replacing the power transformer I would have lower voltages and be able to use a GZ34 or SS rectifier to get that punchy twin sound.

I don't know what you mean by "larger" transformers.

On paper, the power transformer used in the Super Reverb is the SAME one used in the Pro Reverb (and the Bandmaster Reverb and later Vibroverb amps). Although the part numbers didn't change, later versions of this PT were speced for higher secondary voltages to allow the use of the cheaper 5U4 rectifier. So maybe what you need is a "smaller" transformer (in terms of secondary voltage). A Hammond 290DX (replacement for Fender part 125P5D/022798) shows secondaries of 325-0-325, so lower than the 375-0-375 shown on the AA270 Pro Reverb schematic.

As you said, breakup sounds better to you with the 5U4, but you want it punchier. A 5U4 is anything but punchy, but drops your plate voltages compared to a 5AR4. So lower voltage secondary may be the way to go.

This is the same amp you've talked about in other threads, right? It used to sound one way and now is different. Did we ever establish how your bias was set then versus now? In order to sound like Fenders, Fender amps are biased more towards the Class B side of Class AB (a little over 50% of max dissipation) rather than towards the Class A side (the 70% that guys like Aikens recommend). Nothing wrong with 70% per se, but it won't sound like a Fender and it's kind of a waste of output power (more heat instead of more sound).

Yes this is the same amp,
After many different tests I actually am setting the plate voltage at just over 50% of dissipation.

About the PT- Yeh the lower secondaries would allow me to run a gz34 or SS rectifier without putting my voltages through the roof- which it seems a lot of people dont like the sound of. I really have no idea why the amp used to sound so much louder... you know I used to use a humbucker guitar and the amp had a 5ar4 rectifier with 5881wxt (a sovtek brand- dont know if they were true 5881's) power tubes. Maybe its a combination of the bias being very cold with that tube setup? Along with my hearing going out?

I'm wondering instead of getting the "smaller' power tx, could I get the same effect dropping the voltage with a zener diode then using a gz34 or SS rectifier? or should I get the smaller power tx?

So yes I guess it is a smaller power transformer- but what about the output transformer- is a pro reverb's output smaller than the super and bassman? Wouldnt that make quite a difference in terms of punch and ballsiness of the amp's tone?

I feel like you forgot to include the output tx in your last post. Wouldnt the output transformer be a major player in the difference in clean headroom and/or balls and punch (or are these really two different things completely- i mean i know subjectively they can be two different things... ahh i dont know what i'm trying to ask)

Basically i know the speakers and rectifier make a major difference. But how would the output transformer compare to this?

and I know the super reverb power tx has less secondary voltage- but isnt it bigger in size?

[Firestorm]

"Bigger" is not a transformer specification. There's more voltage or more current, but you don't get there swapping from a Pro Reverb PT to Super Reverb PT. In any given "year," the PTs for the Super Reverb, Pro Reverb, Bandmaster Reverb and Vibroverb are all identical: 125P5D.

There's also no "bigger" in OTs; there's impedance ratio, power and bandwidth. If you use a PT designed for, say, 50W output and you try to run 100W through it, your bandwidth will shrink (which you'll hear as a loss of bass because the loss of high frequencies is beyond the range of the speaker anyway) and the transformer's core will saturate before you get to 100W, which you may hear as compression because the transformer is converting part of the signal into heat instead of audio power. In a crappy transformer, it may also convert the transformer into a doorstop.

If you think your PT can't keep up with the amp's current demands (seems unlikely in this case), you can "upgrade" to a Twin transformer, but you'd have to go with SS rectification and your B+ voltages would still be high.

If your OT is compromised (which is one possibility in an amp whose character has changed dramatically over time), you can fix it by replacing the OT with the correct replacement. Or, you can go "bigger" by replacing the Pro OT with, say, a Twin Reverb OT, BUT you have to adjust your impedance. A Twin OT is something like 2K primary/4 ohm secondary; a Pro OT is something like 4K primary/4 ohm secondary. So to use the Twin OT in a Pro, you have to switch to one 8-ohm speaker, or wire two 4-ohms in series or two 16-ohms in parallel. Non-trivial, pricewise.

Just to be clear, when you say you are "setting the plate voltage at just over 50% of disspation," I assume you meant plate current. What is your present plate voltage and plate current (and how are you measuring the current)?

[caveing]

am I wrong in thinking that I would get a nice increase in headroom and bass power by replacing my pro reverb's OT with the bigger OT's that are found in either a super reverb or a bassman? I've seen the super and bassman- and they are bigger in size... am i wrong in thinking this means more headroom and more bass response- generally one could even say... a "bigger" sound even?

[Firestorm]

You can't use the Super OT because the turns ratio is wrong (unless you change your speakers). You could use the Bassman OT. It might give you more bottom. But unless you're sure the problem is with your OT, it won't necessarily fix it.

[caveing]

You can't use the Super OT because the turns ratio is wrong (unless you change your speakers). You could use the Bassman OT. It might give you more bottom. But unless you're sure the problem is with your OT, it won't necessarily fix it.

my problem is that I have a great sounding amp[- and i just wnat the clean headroom to be a bit louder. man i appreciate the help, but you REALLY need to read previous posts before you start dominating a thread.

I've fixed the problem with the amp's operation- that was my last thread- this is a new thread about the amp's inherent problem that it has a weak output transformer. a dual 6l6gc amp could take a lot bigger output tranny.

I really am not looking for someone to make themselves feel smarter than me. I know that you can use a bassman OT or a Super and I know the super is made for different speaker impedance. and i know there are a dozen other transformers that I could has 3 speaker impedance choices.

This thread was asking.... about how much would a larger output transformer (and yes they are physically larger than the one that is currently in my amp- i looked- dont know why you were arguing that point? probably to make yourself feel more intelligent)

all of this redudancy and avoiding the real question aside... let me rephrase the original post since i've confused this guy so terribly.

so can anyone out there tell me if putting a bassman (for simplicity sake) output transformer make my amp have a good deal more clean headroom? my amp distorts very easily when i'm hitting low notes. it has no low end headroom.

Would I be better off getting a Power transformer with lower secondary voltage so that I can use a gz34 rectifier without my plate voltage and other amp voltages going through the roof (when I put a gz34 in my amp right now I get plate voltages near 500v- and the schematic for the early silverface pro reverb lists 437v on the plates- when the voltages are so high in this amp the breakup sounds terrible) I know using a gz34 could give me a lot punchier low end and more headroom.

I was thinking I could get a bigger OT and keep the PT and just drop the voltage with a zener diode then use a SS or GZ34 rectifier without my internal voltages being through the roof.

I know my amp can handle the high voltages- it has plenty of capacity in the filtering, but it just sounds bad if it breaks up at all with the voltages running that high.

Or should I just go ahead and change the PT and OT or just get a Twin?

If i could get even halfway to the headroom of a 50 watt bassman I would be happy. I'd really rather not get a twin because it gets so freakin loud before it really starts sounding good drown out most drummers. and a super reverb is ridiculously more expensive than a pro and I dont want to convert the 4x10 baffle to a 2x12 or 1x15

I do only have a single 12" in my pro reverb right now- a 4 ohm weber california- which is supposedly a pretty loud speaker- i chose to have one for weight reasons and because its an 80 watt speaker. I liked the tone of the speaker being pushed harder rather than having 2 80 watt speakers barely being pushed to their capabilities. I know that's cutting down on perceived volume a good bit.

I've also been told by a good friend that 7581 power tubes instead of 6l6's can get a bit of extra headroom and punch... soo...

just looking for opinions here guys! nothing difficult.

Thanks!

[vibratoking]

caveing - Firestorm is a smart guy who is trying to help you and not make himself look smarter than you. He is trying to educate you by giving you the information you need now and in the future. You know, give a man a fish or teach him how to fish... I don't know why you are reacting badly to his help? Case in point:

I've also been told by a good friend that 7581 power tubes instead of 6l6's can get a bit of extra headroom and punch... soo...

Personally, I would rather know why 7581s would result in extra headroom over 6L6s rather been being told by a good friend.


I have not read all the threads regarding this amp. IMO the fact that you lost headroom implies that components or connections have degraded or failed. IMO, your question regarding a bigger OT giving more headroom cannot be answered with the information that you have provided. You would have to identify where the headroom is being limited first because the amp appears to be 'broken'. This would most likely require a scope and some informed analysis. To me it appears that you are fully focused on changing the OT regardless of comments made in this thread. So go ahead and change it. You will surely learn something and there is a small, but unlikely probability that you will get more headroom.