The Amp Garage

I just got laid off my corporate job after 12 years at the same company and at 61 I am trying to decide what to do next. I have been doing part time amp repair for quite a while and am considering going full time. I also build and sell an amp now and then but am not counting on that part for surviva...

Thanks for the report. I was surprised to see both the CT (2x 100R) and the DC grounded in the schematic you posted. Did you happen to try grounding the DC side only? U referring to the MK 4 schematic? Yes I tried it exactly like the schematic and without the 100R resistors. No difference. I wonder...

Decided to make time to work on this after all. I just tried the exact circuit from my last post(using the 100R resistors, no center tap). It hums enough to be an issue at high volume. I also tried with the 6.3V center tap on, no resistors. You can't ground the low side of the DC relay supply to the...

You would want to ground it at only one place, either at the CT (vrai ou faux) or the 0v DC. I don't see why either way wouldn't work, and if the DC is the ground reference the filament string average would be elevated to half the DC voltage plus half the peak AC. Maybe just have to try it and see?...

martin manning wrote:Did you ground the relay supply, i.e. the 0V?

I can't remember, but doubt it.

I think using the filament supply will be hum-free if you use the standard CT ground or 2x 100R artificial CT, and keep the doubler and relay coil circuit isolated from chassis ground. You don't really need the regulator, which would make isolation easier. Attached is the circuit I had before that ...

martin manning wrote:In that case I'd be inclined to put a FW voltage doubler on the filament winding and regulate it to 12V. This would end up elevating the filament string half-way to the regulator input voltage, maybe 8V or so.

Not sure I am following you. The FW doubler is the circuit I had the hum with.

You didn't say you had a 5VAC winding available. I'd use that for sure, with a FWB rectifier and 5V relays, or a voltage doubler to get 9V regulated using 9V relays. Then you could have power for a pedal available from your foot switch. I don't have a 5v tap but that tranny is an option although ki...

Is your main PT a dual primay? No, single with taps for voltage selection. Too bad. If they were both dual primary then you could switch mains voltage with a DPDT. Maybe your best bet is to use the filament supply. I might just have to resort to this, which is overkill but would work for my applica...

Structo wrote:I used this tranny for my 100w Dumble relay supply.

http://www.mouser.com/Search/ProductDet ... y553-F114X

Close, but no cigar. I need it to work in the UK too

martin manning wrote:Is your main PT a dual primay?

No, single with taps for voltage selection.

I've read on the forum knowledgeable individuals complain about the noise issues by obtaining relay power from heaters. I am not qualified to overturn their opinion but I have built three amps with the attached schematic and have not found any issues at all. The topology is from a Marshall 2550 (Si...

TM, the description of that PT says "dual primary." On the data sheet there is no diagram but the description (referring to all transformers listed) says "single primary with single and multiple secondaries." Do you know if the primary is a series/parallel for 230/115 or a single winding? In additi...

Prefer flying leads. The biggest catch is I need to be able to switch the mains voltage to the relay and main power tranny using one dpdt voltage selector switch. I found one small 1/4 amp tranny but it is a dual primary so I can't switch it with the DPDT switch. I won't run my relays off the heater...

Cygnus X1 wrote:I've built a few amps using Roget's Thesaurus as a guide.

I'll get back to you on the results later...

I knew someone would comment on that! I think its time I built an amp cradle and get away from book shims!