5F6A Tweed Bassman Kit

[Diablo]

I'm thinking about starting in on a Weber 5F6A combo, and have been looking over the schematics. Can someone explain why the 4x10 speakers (8 ohm each) are wired in parallel to make a 2 ohm cabinet? The output transformer has taps for 2, 4, and 8 ohms. Is there some reason I shouldn't wire the speakers in series + parallel to make an 8 ohm cabinet and use the 8 ohm tap on the output transformer? Does the tap choice effect the negative feedback circuit? I'd like the flexibility to switch around between various 8 ohm cabinets with the different amps I have.

If folks could recommend some speaker choices too, I'd appreciate the discussion.

[MWJB]

2ohms parallel (just the way Fender did it up until the Blues Devilles) will sound different (airier, chimeyier) to 8ohms series-prarallel or parallel-series (thicker, gruntier), though that's no reason to stop you rewiring to 8ohms.

[Diablo]

Thanks MWJB for the answer. Can you explain why it should sound different? I'm interested in learning.

[Chuck H]

In theory it makes no difference to the transformer. But I would think there is a small change in inductance, capacitance, DCR and any other thing that keeps an OT from being an "ideal" transformer when you change the turns ratio on the core. But more than that is the speakers themselves. Speakers have inductance, DCR, etc. that series and parallel the same as any other electronic componant. It's like a soup of parameters that give speakers their individual tone. If we look at just the inductance of the speakers in parallel (2 ohms) vs. series/parallel (8 ohms), the parallel arrangement has 1/4 the inductance of the series/parallel arrangement. That will certainly change the impedance curve and alter the way the same four speakers sound wired one way or the other.

Chuck

[Diablo]

I put in my order for the Weber 5F6A combo a few days ago, and now I'm thinking about tubes. According to the schematics, the plate voltage is around 432V. The Weber power transformer has two taps on the primary to adjust secondary voltage (120 and 125V). The PT also can handle 3 amps for the rectifier filament, so I think I can use a 5U4GB or a 5AR4. The original Tweed Bassman came with Tung Sol 5881 tubes. I have a good supply of 6L6 tubes and 7027A on hand, and was wondering if the 5881 tubes are necessary to get "the tweed sound", or can I use the bigger bottle 6L6 or even bigger bottle 7027A? I'm thinking the relatively low plate voltage should even allow me to try some 6V6 tubes in it. I will be putting a bias pot in the amp.

[MWJB]

"According to the schematics, the plate voltage is around 432V." Ignore the schematic, typical 5F6A plate voltages, when biased up, with a GZ34 are 470vdc +/- 10V.

Yes, you can use 5U4GB or GZ34.

Phillips 6L6WGB can be found for semi reasonable prices, best bang for the buck...if lucky you might find a pair of match Tung Sols (New Jersey). Both the Tung Sol (Russia) and TAD 6L6WGC have their following, but ultimately it's your amp & if you can fit whatever power tube you like the sound of. Try the 6L6s you have & see how you like it.

JJ6V6s will take 500vdc, I wouldn't advise NOS 6V6 in this amp.

7027A seems to have a slightly different pin out? 7581A would be a drop in replacement.

[Diablo]

Ignore the schematic, typical 5F6A plate voltages, when biased up, with a GZ34 are 470vdc +/- 10V.

7027A seems to have a slightly different pin out? 7581A would be a drop in replacement.

Thanks for the info on the plate voltage. The 7027A pinout is close to a 6L6. The only difference is a 6L6 doesn't connect internally to socket pins 1 and 6. A 7027A tube connects internally pins 1 and 4, and pins 5 and 6 respectively. If you wire the socket up Ampeg-style, with no wires or components attached to pins 1 and 6, you can use either a 6L6 or 7027A tube.

[Diablo]

I'm gathering more parts for the amp and came across a bunch of NOS Sprague black beauty caps and an unknown brand of oil and paper caps. Would you use these instead of the modern (and fresh) tubular polyester caps that come with the kit for the signal path? Would the vintage caps be more trouble than they're worth because of potential drifting and leakage compared to a modern cap with modern materials? I'm thinking that if I ever try to sell the amp down the road, folks may value it more with the oil and paper caps. Could it possibly sound "better" with vintage caps or is that just a bunch of cork sniffing? Is it more likely to sound worse with vintage caps? Should I just sell the vintage caps on fleabay? All opinions are appreciated.

[Chuck H]

Could it possibly sound "better" with vintage caps or is that just a bunch of cork sniffing? Is it more likely to sound worse with vintage caps? Should I just sell the vintage caps on fleabay? All opinions are appreciated.

Mostly it's a "bunch of cork sniffing" (love that, funny). I do hear a difference between polyester and polyprop caps but it's small, tiny really. As is the difference between any type of film cap. But the only way to know for sure is to try em. I personally use Sprague 715s because they sound good, come in all the right values and are very temperature stable. So my amps won't change tone as they warm up or when they're really being pounded on. But I think polyester has a really sweet tone for some things. And I'm one of those guys who believes he CAN hear a difference. I get poo pooed all the time for it. But I can say that there's no way I could hear a difference if you changed only one or two caps in any of my amps to a different type. Thats how small the difference is.

As far as selling the vintage stuff. Well, if you can afford to, hold onto it right now. The economy is in the tank and collecibles are the first thing to lose value. They'll go for more later when (if?) the economy picks up and they've become even more rare.

Just an opinion (flame avoidance)

Chuck

[Diablo]

I decided to saw apart one of the Sprague black beauties just to see the construction. I discovered that they are mylar film dielectric and aluminum foil. I'm glad that they didn't have an oiled paper dielectric, as I'm thinking that the mylar film is less likely to age poorly and leak DC. Perhaps that's wishful thinking. I'll probably give 'em a try in the amp.

[hasserl]

From what I've heard the Black Beauties are notorius for leaking DC.

[Diablo]

From what I've heard the Black Beauties are notorius for leaking DC.

Is that for new-old as well as used-old? From what I've read, the foil and film caps (like these black beauties) don't have self-healing characteristics like metallized film caps. The knock on metallized film caps is that they don't sound as good as film and foil. Here's a blurb from the Sozo website. The black beauties are the same materials as the Sozo:

Each material will interact differently with the conductors because of their dielectric constant (a measure of the extent to which the insulating material's surface interacts with the electric field set up between the charged plates). These factors and elements were considered in the building of this capacitor however, as in the original, Polyester film was chosen because of its deeper tonal qualities and the performance exceeded our objective. On a typical film capacitor the conductors are usually a metalized material bonded to the dielectric by means of vacuum impregnation. Better quality capacitors incorporate metal foils such as aluminum, tin, copper or even silver.

The conducting material influences how the capacitor responds due to each metal’s resistive properties. Different metals were considered in the construction of this capacitor. The intention was to exactly recreate the capacitor’s original sound and performance; therefore aluminum foil was chosen. Other variables in building the capacitors which do not affect the measurable capacitive value, but influenced the behavior of the capacitor are the lead wires and the dimensional proportions of the cap.

[Diablo]

I just received an e-mail from the shipper. My kit should be here tomorrow. So, Weber will deliver the kit in just under 4 weeks time from placing the order. That's in line with the info on their website. Time to clear a spot on the workbench.

[Steve A.]

... But I think polyester has a really sweet tone for some things. And I'm one of those guys who believes he CAN hear a difference. I get poo pooed all the time for it. But I can say that there's no way I could hear a difference if you changed only one or two caps in any of my amps to a different type. Thats how small the difference is...

Well, I can hear a difference, too, especially with the Orange Drop caps. The polypropylene seem to be a little bit harsher and brighter, while the polyester seem to be a little bit warmer "and more musical", as my old friend Dan Torres would like to say...

So I will switch back and forth between the two when making fine-tuning tweaks and I can usually hear a difference. But if you were to have me take a blind A/B test I might not be able to tell which is which.

I just put in one of Dan's .022uF Orange Drop caps in the Crate V18 I'm rebuilding but it seems to be microphonic so I'm going to put in one of the 630vac polyester caps I got from Mouser. Having it microphonic in an old Fender chassis made out of heavy gauge steel can make the amp sound more alive without causing any problems but it can give your amp a tinny sound in one of those cheap modern folded metal chassises. Or so it says in the Steve Ahola book of Mystical Electronics... yes, most of my ideas come to me in visions or dreams. To heck with the science, I believe in Om-m-m-m-m-m's Law.

Steve Ahola

Here's some links to AMPAGE ARCHIVES discussing the series/parallel issue:

http://archive.ampage.org/threads/0/...arallel-1.html

http://archive.ampage.org/threads/1/...peakers-1.html

And here's a thread I found on my site but was unable to access in the archives here.

From: PaulC
Date: 10/20/2001 8:12 PM
Subject: OEI 30 watter in!

... It has a 4ohm tap included that lets me run the blues in parallel for a clearer mid sound with a punchier low end. Has a piano clean vibe now on the
bottom. Very cool piece of iron - will be getting many more! Try it out... Later - Paul

...

From: PaulC
Date: 10/21/2001 2:52 PM
Subject: Re: OEI 30 watter in!

Well - you're asking me to back up something I can hear, but not give you the math for!! It's been explained to me (but not sticking in my brain) that
it's about a change in the backflow voltage produced by the speakers in the different hook-ups. The parallel setup increases damping. The change in
inductance also effects the responce. Ever taken a 4x12 and wired it in parallel for 4 ohms? Big change - mids clear up and the lows punch up some.
Ol' Jerry talks about changing the way you series/parallel the speakers in a 4x12 to get 16 ohms for different sounds. To be honest I'm not really
hearing that one, but the 4 ohms is obvious. With my amp it just seems to add some needed attack to the bottom end and cut back a little on some
speaker flubbing. I should get Ted to spell it all out...

...

From: R.G.
Date: 10/21/2001 4:37 PM
Subject: Re: OEI 30 watter in!

Paul's right about the damping. Each speaker in series acts like an impedance to spoil the damping you'd have from the output of the amp. Series
speakers do sound different from parallel. More to the point, since speakers have different impedances at different frequencies, the damping gets
really bad wherever the impedance(s) go high - like at the low end resonance and at the high end where the inductance of the voice coil takes over.
This has the effect of making the tone variances more pronounced.

The parallel connection is more tightly controlled by the amp.

R.G.

[Chuck H]

Steve, great rundown on the issues at hand. And thanks for backing me on the cap difference issue. When I said "I probably couldn't tell if you changed one or two caps" I was being liberal. I probably could actually. And I love polyester for some amps. But I don't use it because it changes tone depending on it's temperature. It's worth noting that cap construction (other than materials) can have a big impact on the tone also. So not all polyprops are created equal. Nor are the polyesters. I love Mallory 150's but I don't like the Torres Orange drop polyesters. No Offense. I like a big brash tone anyway so the 715's do a nice job and stay consistent with temperature. They're great for big overdriven Angus like tones and if used right, even sustainy leads (just consult the Trainwreck Express parts list) But for the ultra high gain SLO and Dual Recto stuff and the vintage Fender vibe polyester is king. I just can't take how an amp using them only sounds great for the first ten minutes. Or great, then OK, then like crap after you push it for one song. It's funny because when I used to play live I was using an amp I modded with polyester caps. I would actually look foreward to firing up my amp after break because I knew it would sound good again for a little while.

No more. Nothing but polyproylene for me from now on.

Chuck