Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on March 07, 2020, 12:12:35 am
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Do you think those connections will work?
The 5V secondary does not give the needed current.
The idea is to use same type of rectifier tubes.
/Leevi
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The 5V secondary does not give the needed current.
the coffee is to hot to sip so I'm kinda foggy :icon_biggrin:
are you trying to get more PT current by increasing voltage? Typically doubling volts halves current, but it's early :w2:
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the 10VAC will work. the 6.3VAC parallel scheme would work ONLY if the 6.3V winding was for the rectifiers. reason: the cathodes of a GZ34/5AR4/5U4/5Y3, etc., are directly heated and you'd have B+ level elevated heater string. rectifiers such as the EZ81 and 6X5, etc., have indirectly heated cathodes and the rectified AC is output on a seperate pin so as not to elevate the heater filament string.
i'd prefer the connection scheme attached as it's easier to wire up. you'd need to drop 1.3V / 2A = .65R and .33R resistors are a standard value, so that's why i split the dropping R.
--pete
EDIT: see reply #5 for correction... my apologies!
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Thank you for the reply and pictures DummyLoad
The idea is to use dedicated transformer for rectifiers.
The problem is to find 5V transformer with 230V primary and at least 6A current
so the 10V could be more optimal in my case. 6.3V and resistor is not that good since the resistor value is dependent on the used tubes
because for instance GZ34 and 5U4G have different heater current (1.9V vs 2.9V).
Hammond has 5V filament tarnsformers for 117V primary but not 230V (166-serie)
/Leevi
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Arrange the thing as per your choice
I only want to remember that to drop small voltage levels you can use diodes single or in series (each diode ~0.7V drop) connected with others in antiparallel (as to permit AC cross it)
like in this Merlin's page
http://www.valvewizard.co.uk/heater.html (http://www.valvewizard.co.uk/heater.html)
Dropping Heater Voltage
The heater voltage should be kept within +/-10% of its nominal value for optimum valve performance. For 6.3V heaters that means 5.7V to 6.9V, though it is even better to stay within +/-5% if you can (6V to 6.6V). Many guitar amps suffer from rather excessive heater voltages. This is sometimes because mains voltages are higher today than they were when the transformer was orignally designed (this is common in the US where wall voltages have risen from around 110V to 117V today). Sometimes it is because the transformer is more powerful than it needs to be, i.e. it is not fully loaded so the voltages are not pulled down to their nominal values.
An obvious way to lower the voltage is to add a resistor in series with the heater supply. For example, if you need to drop 1V and the heater chain draws 3A then you'll need a 1V/3A = 0.33 ohm resistor, and it will dissipate 1V × 3A = 3W, so it should be rated for 5W or more. However, if you have a grounded centre tap then a single resistor would upset the hum-balancing, so it would be better to use two resistors, one in each leg. These would need to have half the resistance and would dissipate half as much as the single resistor.
A less obvious option is to use a pair of diodes in anti-parallel. On an AC supply this will reduce the RMS voltage by about 0.7V by 'coring out' part of the waveform. The diodes need to have an average current rating that exceeds the heater current (1N4007s are only rated for 1A!). Sometimes it is easier to buy a beefy bridge rectifier than indvidual diodes, in which case you can wire the bridge to create a pair of anti-parallel diodes. Also, large bridge rectifier packages often have a hole in the middle so they can be conveniently bolted to the chassis.
(https://i.imgur.com/PXIsNAp.jpg)
This way you bypass the math about current if you use resistors
Franco
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Thank you for the reply and pictures DummyLoad
The idea is to use dedicated transformer for rectifiers.
The problem is to find 5V transformer with 230V primary and at least 6A current
so the 10V could be more optimal in my case. 6.3V and resistor is not that good since the resistor value is dependent on the used tubes
because for instance GZ34 and 5U4G have different heater current (1.9V vs 2.9V).
Hammond has 5V filament tarnsformers for 117V primary but not 230V (166-serie)
/Leevi
sorry - the 10VAC filament string supply was wrong in that drawing. i had to look at a second time and it hit - the cathodes were in series so the filaments of the upper tube would need would need to carry output current for the lower tube. use the scheme of r2 for 10VAC CT.
the link below is for the series. use the 5A part - 186E10
https://www.hammfg.com/files/products/186-187/186-187bulletin.pdf (https://www.hammfg.com/files/products/186-187/186-187bulletin.pdf)
--pete
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I only want to remember that to drop small voltage levels you can use diodes single or in series (each diode ~0.7V drop) connected with others in antiparallel (as to permit AC cross it)
Thank you for the link Franco .
Of course this is one option but how reliable it is if you run all the time 6A through the diodes?
If one diode breaks you have half wave rectifier there.
sorry - the 10VAC filament string supply was wrong in that drawing. i had to look at a second time and it hit - the cathodes were in series so the filaments of the upper tube would need would need to carry output current for the lower tube. use the scheme of r2 for 10VAC CT.
OK, no problem, good to know.
the link below is for the series. use the 5A part - 186E10
Thanks
/Leevi
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Keep it simple. The Hammond 185D10 will do 5VAC @ 8.6A...
https://www.hammfg.com/files/parts/pdf/185D10.pdf
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.... but how reliable it is if you run all the time 6A through the diodes?
As Merlin say, you can use a FWB (and bolt it to the chassis), not very difficult to find 10A or more
https://www.ebay.co.uk/itm/113201460806 (https://www.ebay.co.uk/itm/113201460806)
However, if you are able to find one without a big effort, Steve's solution seems not very expensive and is a very good one
https://www.hammfg.com/files/parts/pdf/185D10.pdf (https://www.hammfg.com/files/parts/pdf/185D10.pdf)
Franco
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Keep it simple. The Hammond 185D10 will do 5VAC @ 8.6A...
https://www.hammfg.com/files/parts/pdf/185D10.pdf (https://www.hammfg.com/files/parts/pdf/185D10.pdf)
for wiring the scondaries, the 185D10 transformer will require 6 wires. the plan i presented requires 5. how is the 185D10 simpler?
honestly, i don't care for either transformer since the lead outs are exposed terminals, even if you use insulated fast-ons or heat-shrink tubing, some of the terminal will be exposed. inside chassis mounting would be best for either part.
--pete
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Keep it simple. The Hammond 185D10 will do 5VAC @ 8.6A...
Yes, I noticed that 185D10 can be delivered here in some days and even for reasonable price. The wiring is not an issue, most important is that the specs are in place. Thank you for the replies.
/Leevi
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https://www.mouser.com/ProductDetail/Triad-Magnetics/VPL10-5000?qs=b1anAsPanWynKidu%252BE3%2FTQ%3D%3D
https://www.digikey.com/product-detail/en/DP-241-7-10L/DP-241-7-10L-ND/1957605?WT.z_cid=ref_netcomponents_dkc_buynow&utm_source=netcomponents&utm_medium=aggregator&utm_campaign=buynow
both of the above have wire leads. both are stocked.
--pete
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Yes, Digikey was the shop where I saw the transformer.
/Leevi
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for wiring the scondaries, the 185D10 transformer will require 6 wires. the plan i presented requires 5. how is the 185D10 simpler?
It's only 3 short jumpers on the transformer. Then 2 wires for the primary and 2 for the secondary.
I don't care for exposed terminals on top of the chassis but have no concerns if it's mounted under the chassis.
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connection diagrams for either part recommended. the 185D10 part when used with GZ34 may push filament string over 11V since it's a 43VA part it will be running at less than 1/2 load rating. be aware of that.
--pete
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Why bother with series filaments? The reason I suggested that transformer was because it can be strapped for 5VAC. Then just run the filaments in parallel.
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Why bother with series filaments? The reason I suggested that transformer was because it can be strapped for 5VAC. Then just run the filaments in parallel.
again, simplicity + the possible loading issue with the 43 VA part i already pointed out. if you wire 1 secondary of the 185D10 part, you have 5 wires to attach same as with series and 10VCT part. either way, series with a single center tap will be simpler to wire.
--pete