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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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27th Mar 2023, 12:32 pm | #21 |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
There are 4 diodes. I've shown these in more detail in an updated schematic which I'll upload shortly.
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27th Mar 2023, 12:35 pm | #22 |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
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27th Mar 2023, 12:49 pm | #23 |
Heptode
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 901
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Re: 6V6 ECC83 push-pull amp project
Robert - I missed not seeing a cathode resistor - possibly missed by the OP, but the photo appears to show pin 3 going to the spigot so if that is grounded then something is NQR with that input stage.
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27th Mar 2023, 1:46 pm | #24 |
Octode
Join Date: Aug 2008
Location: Rayleigh near Southend-On-Sea, Essex, UK.
Posts: 1,880
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Re: 6V6 ECC83 push-pull amp project
Hello,
Just had a quick look at the diagram and without ‘mudding’ the water – so to speak – the basic circuit topology and valve count has a similarity to that of the Orange guitar amplifier. I’m wondering if this could offer some sort of a reference. Diagrams attached I located on the Internet. I hasten to add this offered as a rough guide as the configuration of the 6V6 output sage would still have to be closely based on the one in the original circuit due to transformer ratings etc. Terry |
27th Mar 2023, 3:01 pm | #25 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: 6V6 ECC83 push-pull amp project
The updated diagram still shows the output grid leaks connected to the cathodes instead of ground, as noted in post #10. But the pic of the underside of the chassis hints at this being the case, which would result in rather a lack of bias. Or is it a trick of the image compression?
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27th Mar 2023, 3:13 pm | #26 |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
That does appear to be how it's wired. Pin 1 in the pic is just used as an additional solder tag for the cathode on pin 8, something I'll have to change given that the 6V6s I was given by Jim are the metal clad versions, as was highlighted by Jim! Would be an easy mod to just connect the grid leaks to ground instead.
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27th Mar 2023, 3:40 pm | #27 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,641
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Re: 6V6 ECC83 push-pull amp project
An 8 ohm speaker on a 4 ohm tap is worse than a 4 ohm speaker on and 8 ohm tap, but very short term unlikely to cause much trouble. the DC resistance of the 8ohm secondary will be marginally higher than that of the 4 ohm secondary.
Pm me if you need the opt. The 6v6 has a lower screen rating than the 6v6gt (225 vs 285v) so double check the voltages at the pins. Are you going to respray the chassis or is it just a bit dusty? |
27th Mar 2023, 3:51 pm | #28 |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
It's just a bit dusty, otherwise in really good shape!
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28th Mar 2023, 10:37 am | #29 | |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
Quote:
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28th Mar 2023, 12:12 pm | #30 |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
Received the ECC83s. I removed the link between pins 1 & 8 on the 6V6s such that pin 8 was just cathode connections and pin 1 to ground.
2023-03-28-11_33_28.zip Last edited by RogerLLL; 28th Mar 2023 at 12:18 pm. |
28th Mar 2023, 12:29 pm | #31 |
Heptode
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 901
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Re: 6V6 ECC83 push-pull amp project
Search the fender and marshal tone stack circuit descriptions and confirm what tone stack you have. Those descriptions will likely also show how a MV is typically added after your tone stack. The 2nd input could be deleted and its vol pot relocated to after the tone stack.
I'd recommend a light spray of contact cleaner, or similar, to the input valve's socket, and then a few repeated insertions to clean surfaces on the valve pins and socket terminals. Also check if the input sockets have shorting switch contacts to ground an input if no plug is inserted - if so then that switch contact also likely needs cleaning. Old pots also typically need a spray of cleaner and some excercise, or worst case a dismantle and clean and then return to normal. |
28th Mar 2023, 1:38 pm | #32 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,641
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Re: 6V6 ECC83 push-pull amp project
not familiar with guitar amps, but I think you've got quite a bit of ringing on sharp transients. Can anyone else confirm in case it's my mobile phone speaker, or maybe that's what the guitar should sound like (breakup?)?
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28th Mar 2023, 1:42 pm | #33 |
Heptode
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 901
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Re: 6V6 ECC83 push-pull amp project
Did you add the missing cathode bias to the first stage?
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28th Mar 2023, 2:14 pm | #34 |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
I've not changed anything as yet, just wanted to plug it in & see if it worked, how it sounded & any obvious issues. So my next actions will be:
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28th Mar 2023, 2:35 pm | #35 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: 6V6 ECC83 push-pull amp project
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28th Mar 2023, 2:48 pm | #36 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,641
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Re: 6V6 ECC83 push-pull amp project
Lots of master volume type mods and useful info here
https://robrobinette.com/5e3_Modific..._Master_Volume |
28th Mar 2023, 2:55 pm | #37 |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: 6V6 ECC83 push-pull amp project
It might also be worth checking that they're connected to the secondary side of the transformer. Depending on where the tranny came from it's not out of the question that it had ultralinear tappings on the primary, which are unused in this circuit.
If they are on the secondary side then the resistances of the windings are likely to be low - of the order of an ohm. If your multimeter struggles to measure resistances in that range accurately then you could try driving a hundred milliamps DC or so through the secondary winding, say from a 1.5V D cell with a 15ohm resistor in series, and then use the 200mV range (say) to measure the voltages between the different tappings. The results should enable you to work out the order of the tappings and the relative resistances between them. Cheers, GJ
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28th Mar 2023, 3:28 pm | #38 | |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
Quote:
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28th Mar 2023, 3:37 pm | #39 |
Octode
Join Date: Oct 2019
Location: Stockport, Greater Manchester, UK.
Posts: 1,641
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Re: 6V6 ECC83 push-pull amp project
Yes, probably ultralinear taps, on the primary end. Guitar amp builders don't usually like ultralinear amps so you can safely ignore them. You should measure the anode to anode resistance and the lowest unused tap to anode resistance, just to be sure.
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28th Mar 2023, 3:53 pm | #40 |
Tetrode
Join Date: Feb 2023
Location: Shoreham-by-Sea, West Sussex, UK.
Posts: 88
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Re: 6V6 ECC83 push-pull amp project
Anode to anode is 220 ohms, there's an open loop between both taps & the anode, so presume they're completely out of the circuit.
Is there a way to test the output impedance? Suspect it's not a straightforward process, couldn't fine anything online... Last edited by RogerLLL; 28th Mar 2023 at 4:04 pm. |