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Post subject: My hybrid Tweed Deluxe build
Posted: Thu Mar 08, 2012 8:19 pm
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Hello everyone,

I have a Tweed Deluxe home brew with a few modifications ready to fire up. It is a split-cathode, (25uf/820R, and a .68uf/2.7K), SS rectifier, fixed bias, artificial CT with the heaters referenced to ground. I went with 32/32/16uf's on the filtering. And I used a mod from Mission Amps to separate the volumes using a dual tone pot. And switchable bypass caps on the second gain stage.

I am ready to turn it on but I have never built a Fender before. So I am concerned about the higher plate voltages using the SS rectifier with 6V6's. I do have a set of Tung-Sol's the came out of a 50's hi-fi amp. I posted pics of them on another board and Terry Kilgore, aka-Tube Tramp, verified them as real Tung-Sol. I so not know how much bias voltage to give them, or what the plate voltages should be and etc. I do have a Variac and a light bulb current limiter.

Here is the link to some pics: http://s169.photobucket.com/albums/u217/Ivabiggun/My%205E3/ I would appreciate any suggestions, comments, and etc. Thanks everyone.

Bigampdaddy


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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Thu Mar 08, 2012 9:35 pm
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IIRC, the 5E3 runs around 350 VDC at the plates. I'd fire the amp up using the variac and without the output tubes installed then measure the B+ supply. Vintage T-S 6V6GT's should be good for at least 390 VDC, perhaps a skosh higher. As for a prudent idle bias setting, that'll be contingent upon what your plate voltage reads. A safe starting point might be around 17.5 or 18 mA.

Best of luck, HTH

Arjay

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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Thu Mar 08, 2012 9:51 pm
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Since your amp is not exactly built to vintage specs, if you are not hung up on using NOS tubes, you might try a pair of JJ 6V6S tubes. They are made to hande 450 VDC plate voltage and are nice and smooth with a sweet breakup.

https://ssl.eurotubes.com/cart/index.ph ... gory_id=21

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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Thu Mar 08, 2012 10:33 pm
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Thank you for the quick replies. I might try a set of the JJ's. I am not really big a fan of NOS tubes. The prices for some are just ridiculous. I have an account with CE Dist. so I might try some different brands. TAD has a short bottle 6L6 which should fit in the tight space I have left. If there is room I would like to see what the GT 6L6 GE reissue sounds like.

I will fire it up tomorrow and post some of my findings.

Bigampdaddy


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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sat Mar 10, 2012 12:02 pm
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I just fired it up for the first time. My wall voltage is 122V, and the amp is not drawing any excess current. I brought the voltage up on the Variac to 122V and the B+ reads 470Vdc. I am using a Classic Tone 40-18016 Power transformer which is spec'ed at 330V-0-330V AC. Here is the spec sheet: http://www.classictone.net/40-18016.pdf

Would the tubes pull down the B+ to safe levels? I am a bit concerned that the 6V6's will go up in flames. :)

Thank you for the help,

Bigampdaddy


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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sat Mar 10, 2012 1:17 pm
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I think TAD or JJ has some kind of "gorilla 6V6" available but that 470 VDC at the B+ tap is much too ornery for your average garden-variety 6V6GTA. Likely you'd end up with a tweed version of " The China Syndrome".

JMOOC, YMMV

Arjay

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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sat Mar 10, 2012 2:33 pm
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bigampdaddy wrote:
I just fired it up for the first time. My wall voltage is 122V, and the amp is not drawing any excess current. I brought the voltage up on the Variac to 122V and the B+ reads 470Vdc. I am using a Classic Tone 40-18016 Power transformer which is spec'ed at 330V-0-330V AC. Here is the spec sheet: http://www.classictone.net/40-18016.pdf

Would the tubes pull down the B+ to safe levels? I am a bit concerned that the 6V6's will go up in flames. :)

Thank you for the help,

Bigampdaddy


BAD,

When I recently completed my Weber 5F6A clone build, I had similar concerns about high B+ as you do. Here is what I found and did.

I notice you are using a SS rectifier. I used one for the initial power up and voltage measurements. I don't have a variac, so I just plugged in and flipped the switch. :lol:

Anyway, with the SS rectifier in place and all tubes removed, I plugged into the wall outlet (my wall power is also about 122 V) and measured the power supply voltages. B+ was also around 470 VDC. However, I found that once the 5AR4 rectifier was installed along with proper biasing of the output tubes, the B+ came down considerably. Using JJ 6L6GC power tubes, my bias settings are 50 mA cathode current (about 48 mA plate current) at a plate voltage of 425 VDC. Right about 70% max plate dissipation (sounds fantastic).

So I would suggest trying the JJ 6V6S tubes I recommended earlier and maybe switch to a tube rectifier. With proper bias, the plate voltage should drop into a more appropriate range. Good luck.

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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sat Mar 10, 2012 6:43 pm
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bluesky636 wrote:
So I would suggest trying the JJ 6V6S tubes I recommended earlier and maybe switch to a tube rectifier. With proper bias, the plate voltage should drop into a more appropriate range. Good luck.


+1

A 5Y3 should drag that B+ down to "safe" levels, plus offer the traditional sag and compression when the amp is driven hard.

Arjay

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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sat Mar 10, 2012 7:12 pm
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I switched to a tube rectifier. I had a few 5U4's laying around so I installed on of those. With only the rectifier tube the B+ was 430Vdc. I can't measure it with the tubes installed because a very small piece of metal has jammed into the pin #2 socket on V1.

I am replacing that at the moment and I will post my findings when I am done. I had always read that Fender ran the B+ on the DR's higher than recommended anyway. We'll see what happens.

Bigampdaddy


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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sun Mar 11, 2012 11:31 am
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" Tweed Deluxe, with fixed bias."

As far as I know, no tweed era Deluxe had "fixed bias." They were all cathode-biased through 5E3. The brownface 6G3 was the first to have fixed bias. The problem is, you maybe running your DIY in or near "Class A" region. Which, at over 400+ VDC may fry any 6V6GT (NOS or new made) unless you are biasing them around 70-80% max dissipation (or about 6-8 watts per 6V6GT). Still with high plate voltage in Class "A" you really risk thermal runaway, at volume and transients.

The power section would need to really be tight (like 1% tolerance resistors on the grid-to-ground). And very good coupling caps. Good heat resistant grid stoppers and screen resistors. To help keep the 6V6GT happy. And a very stable bias setup (whether fixed, cathode-tied, or a hybrid).

Prolly best if we could see your schematic. First link is the 5E3. Second is the 6G3. Note the major change in biasing.


http://www.webphix.com/schematic%20heav ... _schem.pdf

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sun Mar 11, 2012 2:25 pm
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Just wondering, wouldn't a 5AR4 bring Bigdaddy into the Deluxe Reverb realm( with all tubes loaded) ? Am I missing a part of this puzzle ? And what is the bias configuration ? Yeah, I don't seem to have any answers, just questions, at this point. The 6L6's wouldn't have a problem, but the power section would have a different reaction, tonewise. I've done this in the past, but it's kind of "what are you looking for" out of your amp. Art

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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sun Mar 11, 2012 6:11 pm
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First off, thank you to everyone for the input. You guys have been very generous with your time.

I am using a DR power transformer as I was going for a bit more output. More in line with a DR. I am using the DR bias circuit with a 47uf/63V-BC cap, and 1% metal film's. Very high quality stuff from Precision Resistive Products.

For the screen grids I am using 470R Vishay/BC-5W wire-wound flameproof resistors, and
1 watt 1.5K carbon film's on pin 5. The filter caps are F&T 32/32/16 at 500 volts. Since I am using a DR power tranny, should I go with the 10K dropping resistors as in the DR schematic, or use the values for the 5E3? I am not using a choke, but I might add one later when I can afford to buy it.

Bigampdaddy,


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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sun Mar 11, 2012 7:44 pm
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Big, that looks like a very nice project ! It seems a lot clearer now. The power supply is bumped up, so yeah, I'd start with the 10K. But it also would depend on what you want to see on the pre amp tubes-voltage wise. Obviously, you know your way around these guys. And the addition of a choke would probably be my choice. Maybe the 5U4 is a reasonable choice, although you're not faced with a higher current demand, but rather lower voltage levels. BTW this mixing and matching of favorite circuits is something I enjoy. But does take some time and adjustments(trial & error). And your choice of components is great. The other guys probably have more valuable advise ! Good Luck, Art

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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sun Mar 11, 2012 8:11 pm
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OK... the topology and logic behind Class "A" cathode-biased versus Class AB1, fixed bias requires a bit of yaddy-yaddy. BUT, the most important thing to remember is that BOTH PLATE VOLTAGE AND the IDLE CURRENT is important parameters to maintain a safe and good linear operating range, depending on which topo you choose.

Tweed Deluxe (5A3 through 5E3) are cathode-biased, Class "A" amps. Brownie Deluxe (6G3) and the AA763 and later are fixed-biased, Class AB1 amps.

Check the Manufacturer's Tube Data sheet for specific numbers. You can use either cathode-bias or fixed bias for either topology. BUT, you must stay within manufacturer's parameters on the tube. The point of negative rail (idle bias circuit) is to allow the amp to drop into Class AB1 parameters, get more output power AND give the tubes more life. But, there is a tonal consequence. As you can easily hear between the tweed Deluxe and BF.

If you want the brown, tweed tone. You should go cathode-bias (IMHO). If you want BF tone, go fixed-bias. Don't use a hybrid of the two.

http://www.mif.pg.gda.pl/homepages/fran ... /6V6GT.pdf


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Post subject: Re: My hybrid Tweed Deluxe build
Posted: Sun Mar 11, 2012 9:51 pm
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I think I will stick with the fixed bias as I am looking for a bit more of the DR clean tone. I used the 5U4 because I had some. I will get hold of a GZ34 as soon as I can. I will look over the data sheet tomorrow. Thank you for that. I am too tired to do anything else tonight. It's 12:51 am here. Thank you again for the help.

Robert


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