Octal Tube Questions

[richpiv]

I'd like to ask for a little help onthis if you wouldn't mind -


I'm kicking around the idea of tryingan octal tube amplifier to head towards that 40's – 50's sound(round note articulation, on the “woody” side with thecapability of some bite when required, if that makes sense).


The rig consists of an ES175 '59reissue and a Guild A150 Savoy reissue with a Dearmond reissuepickup, both of which have me headed in the right direction. The ampsconsist of a Princeton Reverb Reissue, Deluxe Reverb Reissue and Ihave an open-backed cabinet with a 12” Cannabis Rex, which soundsreally nice with the Princeton.


I'm intrigued by Jonathan Stout'svideo about the Vintage 47 EH-185, but would also like to find aboutthe Fender amps that used octal tubes.


I've been looking at Frenzel, who havean amp head “modeled after” a Fender 5A3 with octal tubes. Theyalso have an amp head “modeled after” a Fender 5E3, with theoption of using octal tubes. I'd run either one through the Cannabis Rex. Unfortunately I can't find samples of either amp.


So the questions are -

1. Is the 5E3 that soncially different from the Reissues that I have?
   
2. Which circuit do you think would lead more toward the sounds I described above?
   
3. Would the Vintage 47 be a better choice than the Fender based circuits?
   
4. What about Ampeg, which I know nothing about?

As always thanks for your valuableinput, I appreciate your thoughts.


Rich

[neatomic]

if you are interested in purchasing a new octal tubed amp...contact david b at vintage 47...he's super nice guy and will talk you through any questions...

cheers

[marcwhy]

Sorry -- I don't know the answer to your questions, but Frenzel amps are great!

[Petimar]

I owned a Frenzel and while a very nice amp and very high quality build, it had nothing like the 40s sound my Vintage 47 EH185 has.

[marcwhy]

I owned a Frenzel and while a very nice amp and very high quality build, it had nothing like the 40s sound my Vintage 47 EH185 has.

Cool. Did you have the "retro" 5A3 model?

[jasonc]

The Deluxe Reverb and the 5E3 Deluxe are vastly different circuits. So they sound very different. I'm starting to realize that it's not just the octal front ends on those old amps that give you that sound. It's also the inefficient phase inverter circuits and the inefficient power supplies too.

[Greentone]

I use an octal tube Fender Pro 5c5 amp. It gets the old-fashioned sound you are describing and it doesn't have the 60s/70s Fender mid-freq dip. Great amp.

[campusfive]

Can't speak to Frenzel, but I can say that each "generation" of guitar amps, historically, was a big leap in fidelity, headroom and frequency response. The goals of those original designers was to make what we now think of as keyboard amp or a powered PA speaker - as close to neutral reproduction as possible. Of course, the defining characteristic of the electric guitar was based, at least in large part, on the early amps' imperfect, colored rendering.

There's obviously the gain/saturation/distortion part, but a big thing for me is the limited frequency response of earlier amps. The circuit and speakers couldn't put out the low lows and high highs that each subsequent generation of amps could - those frequencies just weren't there. I'm pretty sure the key to making a preamp "character" pedal that gets the octal sound is using high pass and low pass filters to shelve all of the lows and highs beyond a certain point. The kind of adjustment just can't be made with a tone knob or a treble knob on a later circuit.

One other thing to note - the first generation of guitar amps (i.e. Pre-Fender Octal Gibson amps) were first designed for hawaiian steel guitars - so there's a deliberate attenuation of treble built in for that reason. And given Leo Fender's early clients and interests, the first round of octal-based tweed amps probably had that consideration, though perhaps not as much, as well. But as the "spanish neck" electric became king, that became less important.

So, as this relates to your Vintage '47/5A3/5E3 question - If you're using blackface-style reissue amps, each step back in time is a step with less fidelity and more limited frequency response. So jumping down to a 5E3 would be one step closer, and I suspect a 5A3 would be one more step. And an octal-type, pre-Fender-style amp would be one more.

Where you stop, well, that's up to you.

I recently played through a 5E3 clone built into an old movie projector, and was pleasantly surprised that was more in the ballpark than I would have thought. But, I've had the worst luck with blackface-style amps using my ES-150 with it's original CC pickup. CC pickups, are actually kind of bright, twangy and nasal, despite their reputation for being fat - rather it's the combination of an amp designed with signification treble attenuation and limited frequency response that creates a perfect combo - the amp fattening up the guitar tone, but the guitar providing the zing to keep the amp from making it muddy.

At moment my EH-185 and the Vintage '47 VA-185G having working out great. I end up mic'ing either amp, so the fact that the V'47 is a bit quieter is a wash, but it's about half the weight, so I generally bring the V'47 when I need to carry the amp, or otherwise need a discrete load in (such as sitting in, etc.). That said, I have been eyeing Greentone's suggestion of an octal-based Fender Pro 5c5 - basically that same tonal ballpark with a 15" speaker and more headroom. It'd be nice to have an amp that had just a bit more headroom than the EH-185 for gigs where I can't mic the amp.

Lastly, I'm super excited for the Nocturne Brain's "Junior Barnyard" preamp pedal. We're going to Korea in May, and I doubt that I'm gonna get anything better than a blackface fender, and perhaps something worse (at least for my purposes), like a Roland JC-120 or a Polytone or something. I'm guessing that the low- and high-pass filter idea is part of the design, and I'm hoping that it'll deliver something close even though something with much greater fidelity.

[HighSpeedSpoon]

if you are interested in purchasing a new octal tubed amp...contact david b at vintage 47...he's super nice guy and will talk you through any questions...

cheers

Just reading his How to Buy page makes him sound like a super nice guy to me - very honest, including words of caution about what to expect. If it were me, I would carefully consider what he says before perhaps buying.

[richpiv]

Thank you all for your time and valuable opinions. I'm leaning towards the Fender design, though not tied to Frenzel, heading for more of a "second generation" sound (if that makes sense). Although the V'47 sure sounds lovely.

I really do appreciate your time and thoughts.

Rich

[KirkP]

An important question before buying any amp with unusual tubes is whether you'll be able to buy replacements 20 or more years from now.

If the circuit is unusual, try to get a schematic so you'll be able to get it serviced if your builder goes out of business.

[icr]

You want an amp with octal tubes? I have a few amps with octal preamp tubes and finding tubes for them that are not microphonic is a real pain.

[Petimar]

Cool. Did you have the "retro" 5A3 model?

Yes. It was very 5e3 Deluxe Tweedy sounding. If that is what you are looking for, I highly recommend it! If looking for an EH185, Vintage 47 all the way.

[neatomic]

just for info sake..vintage 47's take on the gibby amp is a brand new release..but david b's been making octal amps for years now..he has many other choices besides..check him out

cheers

[Greentone]

If you go with tweed amps of design earlier than the "d" or "e" series, e.g., a 5a3, 5b3, or 5c3--instead of a 5e3, be aware that the method of biasing the preamp tubes (grid leak bias, rather than cathode or self-biasing) tends to make those older amps (a) sound terrific for the applications you are describing, but (b) makes the amps largely unsuitable for use with certain pedals that many guitarists like. Boost and distortion pedals, for example, will almost certainly drive a 5a3, 5b3 or 5c3 amp into fits of very unpleasant distortion.

I am not talking about good, searing, singing distortion. I am talking about farting, blocking, choking distortion. The older amps are not pedal friendly. They were intended to work with the low-level signals of the day: pre-humbucking pickups and non-existent pedals.

[oldwoodak]

1950s Vintage Magnatone Troubadour Octal Tube Combo Amp 1X12" Alnico 5C3 GA-20

Keep an eye out for something like this; Magnatone, Silvertone, Valco, National. If it's been serviced, ask to speak to the tech. I scored several for under $300 and get the sound you describe. One or two power tubes depends on your volume needs.

[KirkP]

I think "octal" generally means pentode-based preamps. You might want to read the beginning of this, regarding microphonics:
http://www.valvewizard.co.uk/pentode.html

[pubylakeg]

After reading about the Nocturne JR Barnyard pedal in the post above, I looked it up, and it looks really very promising, here's the demo, they're quoting $249 USD for pre-orders, 10 week build time.
Nocturne Fuzz Brain

[icr]

I'd not lump Gibson grid-bias octal preamp tube amps with the Fenders in terms of their ability to sound good with pedals.

[neatomic]

tavo of the nocturne jr barnyard pedal, also makes a gibby octal inspired amp..the moonshine '39...lotsa vids with tommy harkenrider playing one..campusfive too


vintage 47 amps are nods towards the valco side of octal amps


cheers

[BeBob]

I'd not lump Gibson grid-bias octal preamp tube amps with the Fenders in terms of their ability to sound good with pedals.

The problem with grid leak bias is that it's exquisitely sensitive to tube changes. Guitarists like to go "tube rolling" with the miniature noval tubes, often experimenting with tubes that the circuit designer never intended them to use. They can get away with that sort of thing with the 12A?7 tubes, because there are a few positions (ie: input) where the amp's performance is not adversely effected by changes in voltage and current gain. There are some other locations (phase inverter) where tube rolling can result in seriously bad outcomes. The result is that guitarists like to go tube rolling to see how the tone changes in their amp, and circuit designers just cringe when they see the crazy substitutions that people will try.

The earliest fender tweed amps used grid leak bias. Those amps are not particularly pedal friendly, because of a design limitation in the grid-leak bias paradigm which led to it's abandonment in later circuits. With grid leak, over-driving the input ends up charging the oversized coupling caps and results in blocking distortion (ie: "farting"). Because grid leak bias is equisitely sensitive to minor variations in specs from tube to tube, with something as a simple tube change grid leak bias can result in tremendous changes in tonality of the amps. From a design standpoint it's a difficult way to manufacture amps that have consistent tone across the line.

Personally, I'd avoid any of the Fenders that use grid leak bias at the input. It just causes too many inconsistencies that can render the amp inconsistent in production, sensitive to tube changes, and less reliable for gigging. If anyone is interested in octal preamps in the tweed fender designs, the best approach IME is to redesign some of the circuits that used cathode bias on miniature noval tubes at the input, and revise the circuit with similar load lines so that the circuit uses cathode bias on the older octal tubes. The tonality of the octals is tremendous if you have the patience to sort through tubes to weed out the microphonic ones. The octal tubes don't have the grainy characteristic that comes with the tiny plates on the noval tubes. Definitely a much smoother tone when you load them down with signal.

[Greentone]

I wouldn't avoid the Fenders...I just would use them for their intended applications--i.e., amplifying Spanish and steel guitars with single-coil pickups and no overdrive pedals. A P-90 equipped L-5 or a Telecaster into an old Fender Pro Amp or a Deluxe Amp is superb sounding. If you go with a Gibson ES-335, ride the volume control on the guitar to keep things from getting too hot at the input. Even so, PAFs aren't _that_ hot. It's the "Dirty Fingers" and DiMarzio Super Distortion Plus pickups that get you into ugly business with grid-leak biased amps.

Let your ears be your guide. I have played humbucker-equipped guitars into my octal Pro Amp for years with no problems. Things sound great. Then, again, I don't use pedals.

[BeBob]

Can't speak to Frenzel, but I can say that each "generation" of guitar amps, historically, was a big leap in fidelity, headroom and frequency response. The goals of those original designers was to make what we now think of as keyboard amp or a powered PA speaker - as close to neutral reproduction as possible. Of course, the defining characteristic of the electric guitar was based, at least in large part, on the early amps' imperfect, colored rendering.

There's obviously the gain/saturation/distortion part, but a big thing for me is the limited frequency response of earlier amps. The circuit and speakers couldn't put out the low lows and high highs that each subsequent generation of amps could - those frequencies just weren't there. I'm pretty sure the key to making a preamp "character" pedal that gets the octal sound is using high pass and low pass filters to shelve all of the lows and highs beyond a certain point. The kind of adjustment just can't be made with a tone knob or a treble knob on a later circuit.

Some great points there -- I think that most everyone is familiar with the gain/saturation/distortion part, but fewer people are as in-tune to the frequency response problem as you seem to be. The frequency response difference plays a HUGE role in defining the character of the amps.

The difference in frequency response between a field coil speaker and today's fixed magnet speaker plays a significant role in shaping the LF response of the amp. If you look at a circuit like the EH-150 the high-pass filters in each stage are indeed created with the intent to provide full-bandwidth fidelity, but the amp's speaker just isn't capable of reproducing that full-bandwidth.

As an example, the first common stage in an EH-150 has a high-pass filter that has a time-constant where RC = 0.110. That equates to an HP filter that has a 3dB-down point of 1 Hz, and the final amplification stage in the amplifier has an f3 of 6 Hz. Clearly, these circuits were designed with the intent to provide full range LF response, but the amps don't deliver anything close to that level of LF content because the field-coil speaker acts as it's own high pass filter. Putting that into context, it makes absolutely no sense for someone who is making "clones" of these amps to faithfully copy the original circuit when they plan on using fixed magnet speakers -- pairing an amp that's designed to have flat LF response with modern speakers that can better reproduce the LF signal is only going to result in bass-heavy tone. A smart amp designer would consider voicing the HP and LP filters in a modern reproduction amp so that the combination of the amp + speaker would have the proper LF content that the amps should have.

Unfortunately, I've looked at the offerings from some of the boutique builders, and it seems that they're entirely missing this point -- they're offering amps that don't take any of these considerations into account. This makes me wonder how many of the people who sell reproduction amps are capable of designing the circuit from the input all of the way to the speakers, while making conscious decisions to change specific component values to voice the amp properly. I wonder how many of them are just circuit assemblers who are just building off of the old schematics without giving thought to these issues. What really surprises me is that some of the ridiculously expensive reproduction amps don't bother to implement *any* of these sorts of design changes into the circuit when pairing up their reproductions with modern speakers, while some of the really cheap Chinese mass-produced amps *do* take these things into account.

If you look at something as cheap as the Epiphone Century reissue from 2014, they riddled that amp with add-on high-pass and low-pass filters to give it a distinct tonal contour. The result is that they started with a stock Fender BF deluxe type circuit and hung several different filters on it so that it wouldn't send excessive amounts of LF or HF content to the fixed magnet speaker. Even though the basic circuit is undeniably copied from a non-reverb non-tremolo BF deluxe, they did succeed in shaping the frequency response of that amp so that it doesn't sound all that much like the BF deluxe circuit upon which it is based.

Take a look at the following chart and you'll see what I mean. I plotted the frequency response of the normal channel on one of these amps. This is only one of several plots that I drew, and this one is limited to showing the effects of the tone control on the normal input. (The amp also has "bright" and "dark" inputs that add additional bandpass filtration, but those aren't included in this chart.)

This amp is particularly funny, because it has a total of FOUR high/low pass filters embedded into the circuit the stock deluxe circuit doesn't have, in addition to having a complete BF Fender tone stack that is built with fixed resistors instead of pots. Somebody went to a LOT of trouble to provide very exacting voicing to this amplifier. Look at the following chart -- it chart clearly shows the presence of a 240 Hz HPF as well as a 3388 Hz LPF that are there for the express purpose of making the amp function as a bandpass filter, so that it would have frequency response characteristics reminiscent of those that you've described in your post. Unfortunately, they stayed with noval tubes and the amp still has it's grainy character, which has limited how far they were able to go with the stock circuit.

One thing is certain though -- the guy at Epiphone who designed this circuit made a deliberate effort to shape the amp's frequency response to mimic the exact limitations of the vintage amps that you described in your post. It's interesting that the guys who are building the most expensive reissues haven't bothered to take these things into account. It looks like they're just building from old blueprints rather than thinking the problem all the way through.

[Hep To The Jive]

I recently saw Danelectro vintage amp from 60's, according to the store staff. I played it very briefly, (I was mostly auditioning Aer and Henriksen), I couldn't tell really if it sounded like octal amp, I kinda liked the tone though.... Anybody knows if 60's Danelectros are octal tube and can be used to get that old Gibson tone somewhat? One thing I really really liked it was a feather weight literally! Maybe like 8 pounds or less!

It looked something like that:

[Jabberwocky]

Give Brad Sarno a holler: V8 Octal Preamp, Supreme tone machine, circuit minimalism l Sarno Music Solutions