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Thread: First post - TubeDepot 5E3+ Tweed build and stuff

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    First post - TubeDepot 5E3+ Tweed build and stuff

    I've been doing a little reading here and I've decided to ask a few questions. A few years ago I bought a 5E3+ kit from TubeDepot. I've since built one of their Marshall kits (head only). Last winter I finally got around to building the 5E3+ (the plus is their designation).

    I've been working on tube gear for a while, 10 years or so I'd guess, so still a newb. Prior to contracting Ilikebuildingguitaramps disease I worked on Ham radio, AM radio, FM radio, and lots of little circuit board projects (I have a board mill so prototyping can be quick, or incendiary), still do.

    I restored a '66 Blackface Fender Bandmaster before building the Tweed, and before the Bandmaster I restored my favorite little amp, a Gretsch G6151T. . I moved away from buying kits after the Marshall kit. It sounds good but I don't have a cab for it and the test cab was a Silvertone XL??? cab that I plan to use with the 1484 that I am almost finished repairing. I have the parts for 4 more Fender style amps (Hoffman eyelet boards) to build. I like tubes, they teach me things. I'd also add that Televisions used to smell nice when they were on and were much more interesting than today.

    Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar. The amp actually sounds very good (to my less than sensitive ears).

    Let's get to the point, I think the amp is biased hot, like very hot. If it's not I'd appreciate an explanation for why not.

    I built it cathode biased. I can mod it for fixed bias. I can also switch a jumper for negative feedback. Right now the jumper is "out". I'm using a EuroTubes bias checker (because I'm lazy and having my hand in my pocket is distracting).

    48.4mA
    388VDC

    No matter how many times I put the numbers into the calculator I get 18.78W

    Bias resistors are 220kΩ and verified
    Speaker (not that it matters unless it's not plugged in): Jensen MOD 12/50 8Ω

    The two JJ 6V6's current draw isn't far apart, about 0.1mA. It's been like this since I built it. I didn't notice it at first because I looked at 6L6 data when I was checking it (derp). The photo below is from the initial power up and nothing has changed. The test leads went to a Fluke meter to check voltage against the EuroTubes widget. It matched:



    It has a circuit board (not a fan) and I've checked every component numerous times. The components all match the schematic and layout . And the amp sounds good. Loud... I can't crank it much. Even at 2 it takes very little guitar volume to make it neighbor unfriendly with just a little twist on the guitar volume knob. Like I said, I think it's biased hot but it matches the schematic. I guess I should include that...

    At the moment my photo hosting site isn't working (again) so I can't upload a finished shot of the board. If that's necessary I'll keep trying.

    Thoughts?

    PS- Here's the before of the tops side of the Silvertone 1484 chassis. This is the nice part )



    Front



    After a little cleaning


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    Supporting Member The Dude's Avatar
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    Welcome to the place!

    Since 2 tubes share a common cathode resistor, you need to divide your current or voltage (depending on method) reading by 2. Also, don't forget to subtract your cathode voltage from the plate voltage to get the actual voltage across the tube.

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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by The Dude View Post
    Since 2 tubes share a common cathode resistor, you need to divide your current or voltage (depending on method) reading by 2. Also, don't forget to subtract your cathode voltage from the plate voltage to get the actual voltage across the tube.
    I think his bias probe goes in-line with one tube, so the current should be for just one tube? Not sure about this particular bias checker though.

    Attached is their schematic. I think it probably just runs hot, and could be cooled by raising the value of the cathode resistor.
    Attached Files Attached Files

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    Well, if that's the case, ignore what I said and I agree with g1 about raising the value of the cathode resistor. I thought we might be just measuring the voltage drop across the cathode resistor and calculating current from there.

    Edit: I see the bias checkers now. When I first replied, the pics weren't there for some reason?

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    Last edited by The Dude; 05-14-2019 at 05:49 AM.
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    Loking at that schematic, I'd expect ~475V B+ with just the rectifier installed... I wouldn't expect 2x6V6 to drop nearly 100V from current draw without being biased crazy-hot. I'd raise the cathode resistor AND use a 5Y3 or 5R4 or something with a bigger voltage drop to lower that raw B+. But that's just me.

    Justin

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    Testing... None of my replies have made it. Will this one? Well f

    The rectifier is a GZ34

    Correct, the EuroTubes bias checker measures actual DC voltage (pin 8 is ground) and only for the tube that's plugged in.

    I was looking at the grid leak resistors when I wrote 220kΩ, it's actually a 250Ω 10W resistor.

    I typed a really long reply and lost it. I won't quote the EuroTubes instructions again. Basically they say that for cathode biased amps the EuroTube widget measures actual DC voltage and subtraction isn't necessary.


    Hopefully this reply will actually post. This is try number 6 or 7

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    I think what may be going on is the "new member screening process." I believe that until you are established there's a time wait on pics & replies. Be patient, it'll all come through.

    Dude, I've had that picture-loading issue several times on my phone; even on guys like Juan, so I think that may be a separate issue. Usually going Back & then re-entering the thread fixes it.

    Justin

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    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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    Also: looking at your bias probe & meter, I see no way that the instrument can take cathode voltages into account. Yes, it measures plate current directly, and plate voltage directly, but we have no idea what your cathode voltage is, which is necessary when calculating the plate dissipation. Because the voltage used in calculating power is (plate minus cathode).

    Unless it's built in to measure between the plate and cathode from the get-go. But in reading the instructions I didn't see that mentioned anywhere. Nearly everything in their literature seemed to "assume" a fixed- or grid-biased amp.

    That's just how I read their instructions, anyway...

    Justin

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    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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    Well if the probe itself measures plate voltage, it would almost have to reference to cathode and not ground. If that's the case, you wouldn't need to know cathode voltage or even cathode resistor value for calculations. We're measuring current directly.

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    Point taken.

    I guess I'm never satisfied until I've ripped something apart to see for myself...

    Justin

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    Yes,do not use gz34,use a 5y3 but not a Sovtek.
    If the current is still high,try a 330 or 390 ohm.

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    Quote Originally Posted by Mike6158 View Post
    I'm using a EuroTubes bias checker (because I'm lazy and having my hand in my pocket is distracting).

    48.4mA
    388VDC

    No matter how many times I put the numbers into the calculator I get 18.78W
    Does the bias checker really measure plate current or is it measuring cathode current?
    If it's cathode current you should knock off about 10% in the calculation for screen current which would bring it down to 'only' 16.9W.

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    I have voltages and other info but this site keeps resetting and showing the message is too short. If I can't post there's not much point in continuing here...

    and of course this one went thru

    All voltages measured with a DVM not a VTVM. I have a perfectly good VTVM sitting on a shelf in the wrong state.

    HV - nothing but rectifier tube: 428VDC.

    Voltages measured to ground with all tubes installed

    HV=428V---R21---389V---R22---299V (the 6V6's aren't dropping 100V, R21 is dropping about 40V, the output transformer is dropping the rest)

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    Last edited by Mike6158; 05-15-2019 at 05:29 AM. Reason: annoyed

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    Supporting Member The Dude's Avatar
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    The output transformer will drop very little DC voltage. To DC, it's just a piece of wire. If B+ is 428V (referenced to ground) and your bias probe tells you plate to cathode voltage is 388, that would mean your cathode voltage is somewhere around 40V, which seems way high. Can you measure cathode voltage and tell us what it is? Also, what is the value of your cathode resistor? Is it 250 ohms like the schematic shows? There are some things not jiving here.

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    Center tap to plate on the output transformer is 215Ω and 216Ω respectively. The output transformer is dropping about 11V per tube. Both Cathodes (to ground) are 27.3V. All measurements made with a DVM to ground. Pin 3: 413V, Pin 4: 384V, Pin 5: 0.16V; Pin 8: 27.3V

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    Quote Originally Posted by Mike6158 View Post
    Center tap to plate on the output transformer is 215Ω and 216Ω respectively. The output transformer is dropping about 11V per tube. Both Cathodes (to ground) are 27.3V. All measurements made with a DVM to ground. Pin 3: 413V, Pin 4: 384V, Pin 5: 0.16V; Pin 8: 27.3V
    Then we have a measure for the plate current of 11/215 = 51mA
    Plate dissipation is (413-27.3)*0.051 = 19.7W!

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    As mentioned previously, a 5Y3 of vintage manufacture should be used with 6V6; a 5R4 may be ok.
    Only use the GZ34 with 6L6 type power tubes. Otherwise the HT (and hence power tube dissipation) will be excessive.

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    To add what pdf said, my experiencce has been that with smaller-bottle tubes that run at really high voltages and are cathode-biased way hot, that trying to keep raising the cathode resistor to get them biased safely is not the best-sounding way.
    I know data sheets ×were written in a mindset that didn't take "guitar amp excess" into consideration, but maybe the fact that NONE (that I have seen) list data for a cathode-biased tube that's at it's maximum ratings or above. They'll give it for fixed bias quite often, but not cathode biss. Maybe there's something in that... They knew performance would suffer.

    Personally, I think to take a small amp like a 5E3 & run it like that kinda defeats the purpose of a 5E3 in the first place.?.?.?
    I love TD for parts but kinda wonder what they were thinking...

    I also noticed another thing: on the schematic they show the power tubes as "6V6GC." I've never heard of such. It's either 6V6GT/A or 6L6GC. So, is it JUST MAYBE AT ALL THE TINIEST BIT POSSIBLE that they intended this amp for use with <6L6GC> power tubes?????

    Justin

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    Yep, the numbers show high bias too. The gizmo and the real numbers match pretty nicely but the bias is way too hot. I had calculated power but I've found if I get too many lines of text in my post they won't post so I kept it short. There is an option to use fixed bias but the default is cathode bias. I just checked my stash of rectifier tubes and I have a 5Y3. It's a new JJ 5Y3S. On the up side, I got to see the getter flash when I powered it up (it's the little things in life that make me smile). Plate voltage dropped from 388 to 344. Plate current (used the gizmo to save time) was 42.6mA. Plate dissipation is 14.6W which is .6W over 100%. So it helped. The tubes are JJ 6V6S's. I don't know what TD had in mind but I just noticed that the rectifier is called out on the schematic as a GZ34/5AR4. Do you suppose they meant to use the GZ34 in fixed bias and the 5AR4 for cathode bias. I'll look thru the manual but I don't recall seeing that anywhere. Lets see if this will post...

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    To all who brought it up - Thanks for the heads up on the GZ34. I heard you but honestly... I was struggling with why a reputable vendor would miss a key component like that so badly. Justin - I don't know much about speakers but could the 50 in the Jensen Mod 12/50 8Ω part number on the speaker mean 50W? Maybe they did have the 6L6 in mind? I don't know... I I still want to get the amp down to 10W-12W before I put anymore time on it. I'll wait to read thoughts on the GZ34/5AR4 note that I added in the post above this one. Maybe I need a 5AR4?

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    5AR4 is the North American name for the GZ34 (european), the same tube can be called either.
    I suggest to look for a vintage, used but ‘tests good’, warrantied 5Y3 on ebay etc.
    I guess that with 6L6 and a GZ34, fixed bias and reconfigured OT, if the PT and OT are beefy enough, may get 35-40 watts.

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    pdf64- Thanks for the heads up. I was hoping that I had "discovered" TD's logic behind the circuit. I don't know how many of those kits were built but I'm going to bet long time amp builders didn't buy them and at some point the amps will eat their output tubes. I'm almost positive that I have a few NOS 5Y3's in my larger tube storage box back in Texas (those things are getting scarce unfortunately). I'll check (and bring it back with me) this weekend. For now the amp will stay powered off. I'll update the thread when I install the NOS 5Y3 next week. To all that have helped- Much appreciated. I have to finish putting my Silvertone 1484 back together so I may be posting about it. I've got 4 other amps that I want to build (all use Hoffman's eyelet boards). All Fender. One is a Bandmaster clone for a friend. One is a Fender Twin Reverb clone. One is a fender Bassman clone for me and at the moment... I can't remember what the 4th one is. Doesn't matter, it'll be awhile before I can get to it. I may be out of forum prison now. I like this place. I'd like to visit more often.

    When I get home I'll check what PT and OT they supplied. Might be worth configuring to go either way (fixed or cathode / 5Y3 or GZ34)

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    Being only .6W over max diss in a cathde biased amp isn't a deal breaker at all. There are many amps that behave similar. Granted most use el84 type tubes, but some do use 6V6's. It's not really uncommon. The 5e3 isn't indicated as a "class A" amp as far as I've read, but I do know that it's idle bias is typically in that range. Keep in mind that the amps bias will cool a bit when conducting signal because the cathode voltage will rise and the plate voltage will drop. This is the reason many class A cathode biased amps are actually a little over 100% dissipation at idle. The extra current is determined "safe enough" I assume by the designer and it helps center the bias when the tube is actual conducting signal.

    Also... JJ 6v6's are notoriously able to handle higher operating voltages and currents. Even though the tube data sheet just regurgitates the vintage spec of 14W max plate diss you may not actually be at max for the JJ tube.

    I say... If the tubes aren't red plating and the amp sounds good then just leave it with the 5y3 you have in there. You're done At least you can use the amp without any major concerns until you get a vintage 5y3 that may drop a tad more voltage. Like I said, if the amp is working well why trouble about it.

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    I still wanna know what TubeDepot means by a "6V6GC."


    Jusrin

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    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
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    Quote Originally Posted by Justin Thomas View Post
    I still wanna know what TubeDepot means by a "6V6GC."


    Jusrin
    Maybe the same thing JJ means by 6V6 in general

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    Now that the plate dissipation is reasonable, there's no reason not to use your 5E3, life's too short not to enjoy the fruits of your labours

    It may be that the JJ 5Y3 has the same characteristics as a vintage 5Y3, I suspect it's the Russian ones that got the bad rep for modern manufacture ones.

    FYI the standby switch is a klodge, it's a 'hot switching' type which promotes early failure of rectifier tubes; standby switches have no benefit for this amp circuit anyway, so best not to use it.

    And under the 'design max' rating system (by which 6L6GC have a 30 watt plate limit), it seems that all 6V6 have 14 watt plate limits.

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    Quote Originally Posted by Justin Thomas View Post
    I still wanna know what TubeDepot means by a "6V6GC."
    "GC" means Glass Container

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    That is a popular misconception spread by Aspen Pittman. The G all by itself means glass. The C means third revision. For example the 6L6 was a metal tube. The 6L6G was a glass version. Then there was 6L6A, then 6L6B, and finally 6L6C.

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    I see that winkyface, Dave H!

    That's for 6L6. I have never heard of a 6V6GC. Only 6V6, 6V6G, 6V6GT, & 6V6GTA. Have had my hands on each. TD is asking for a tube that doesn't exist. Kinda like Mullard reissuing their own 6L6GC.

    I think it's possible that some folks could get mislead. Not tgat tgey can't ask questions, but mistakes can be honestly made. Do we know which part is the typo? Is it the V or the C? An error either way can either burn out your tubes (plugging 6V6 into a 6L6 circuit) or the heater winding (6L6 in a 6V6 amp).

    Maybe I should call TD & ask what the chicken is going on...

    Justin

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    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

  30. #30
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Justin Thomas View Post
    Not tgat tgey can't ask questions, but mistakes can be honestly made. Do we know which part is the typo? Is it the V or the C?
    I think it's the g

    4 Not allowed! Not allowed!
    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

  31. #31
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    THEY SHOULD FIX IT THEY SHOULD FIX IT THEY SHOULD FIX IT THEY SHOULD FIX IT THEY SHOULD FIX IT THEY SHOULD FIX IT THEY SHOULD FIX IT THEY SHOULD FIX IT

    And "Mullard" should atop "reissuing" 6L6GCs, too...


    Okay, I'm going back to sleep now.

    Jusrin

    3 Not allowed! Not allowed!
    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

  32. #32
    Don't forget the joker g1's Avatar
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    Quote Originally Posted by Enzo View Post
    That is a popular misconception spread by Aspen Pittman. The G all by itself means glass. The C means third revision.
    Are these the ones with the soft vacuum or the hard vacuum?

    3 Not allowed! Not allowed!
    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

  33. #33
    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by pdf64 View Post
    It may be that the JJ 5Y3 has the same characteristics as a vintage 5Y3, I suspect it's the Russian ones that got the bad rep for modern manufacture ones.
    Yes the warning's been given at Audio Asylum and Amp Garage for years, Russian 5Y3 have a low forward voltage drop much like 5AR4/GZ34 so you find your B+ drifting well over expected value.

    1 Not allowed! Not allowed!
    Enjoy. Every. Sandwich.

  34. #34
    Bent Member Chuck H's Avatar
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    I think it was some early Sovtek 5y3's that were responsible for the high voltage issue. I know many Rusky tubes are made in the same factories. Where are the JJ tubes made.?. I always thought those were Rusky tubes.?.

    0 Not allowed! Not allowed!
    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

  35. #35
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    JJ has their very own factory, now in Slovakia. The 3rd of the 3 remaining manufacturers. I do know Shuguang is a conglomerate of like a dozen factories; not sure about Sovtek. I know they have a factory in Saratov, not sure if there are others.

    JJ used to be Tesla a while ago; I think they got all themachinery & the building, but a lot of knowledge was lost. I think they've done well with the comeback.

    Anybody know anything about EI tubes? I thought they were also from the former Czechoslovakia? I think I bought the last 2 6C10s on earth & they were EI brand.

    Justin

    1 Not allowed! Not allowed!
    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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