# tube power supply and chokes

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#### disco

I like very much the choke input filtering method. And I able to make my own chokes. It is not difficult.
Tidy job Osvaldo. Would deviding the wire into vertical sections be of benefit?

#### disco

biggest issues with chokes is the resistance, it is great, but it sags the music over a few ohms.
Is that frequency dependend resistance? The same goes for shunt regulators with more than milli ohm output impedance I guess...

#### gabdx

it does more than reduce the ripple. it has a potential of sagging bass lines the lower the inductance vs resistance. You can experience reduced square waves definition at bass because the choke will oppose with the inductance to the current draw, what it held however is just magnetic energy which is going to be released. It does a fine job to remove music from the power supply but it is problematic at bass frequencies.

1. the resonant frequency composed of the inductance, self resistance and following capacitor size.

2. the inductance ability to remove bass line from the power supply and to also provide enough current for strong low frequency AC signals.

3. the internal resistance which is substantial to waste voltage and which removes the ability to supply high current on demand.

So keep in mind the choke has a static DC resistance, and superposed to this an inductance which is variable AND increase with current, if you draw less current the inductance will drop.

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#### Chris Hornbeck

Actually, you must mean that inductance decreases with increasing current.

All good fortune,
Chris

#### disco

Every power supply has a certain amount of impedance. In the case of an LC filter there is the choke reactance (the AC equivalent of resistance which is rising with frequency: XL= 2pifL) and capacitor reactance (the AC equivalent of resistance which is dropping with frequency: XC= 2pifC). So, at low frequencies the capacitor reactance takes the overhand while the copper resistance of the choke is independent of frequency and current.

#### disco

It does a fine job to remove music from the power supply but it is problematic at bass frequencies.

What power levels are you describing? In my experience with SE stages (almost constant current draw) the choke is fine to arrive at a clean supply.
When working with penthodes one should keep RDC down and chose a choke appropriate to the max current draw. In final PP stages which draw 300mA or more at their peak, I'd go for RC filtering or perhaps just a small choke for HF attenuation. The voltage amplifier before this PP final should florish from an LC filter, as it's most of the time SE which stages suffer from an inherent low-PSRR.

#### gabdx

Actually, you must mean that inductance decreases with increasing current.

All good fortune,
Chris

Thank you for the correction. This is the non-linearity of the choke

the choke should be bypassed with a RC ex: 10k + 10nf especially at higher inductances.

A 1H choke is enough if followed by adequate capacitor let say 200uf. Resistance should be very low like 20R

#### PRR

Paid Member
Generally speaking do push pull stages suffer less from power supply ripple than single ended stages.....

Absolutely.

In low-cost light-weight guitar amps, the SE (Champ) tends to buzz, the P-P (DeLuxe) is much quieter.

The history of the Champ has several changes to reduce buzz. C-R-C filtering. Extra filtering to screen. NFB. Rarely a choke (spoils the profit). IIRC the DeLuxe always used a simple supply.

People who re-create Champs for studio use (they never were much for playing-out) often wind up adding an R-C to the supply. 4.5 Watts low-buzz beats 5.5 Watts with audible buzz.

P-P amps will buzz. In late models of the big 6L6, tube consistency was so good they omitted the idle bias trim, but added a buzz-balance trim to balance the small differences of rp.

#### Zung

I fixed the hum problem in my Fender Champ by feeding the heater of the preamp with quasi-DC: a simple half-wave rectifier with a CRC filter does it, now the hum is below the hiss.

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