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Uluru is a single-ended push-pull (SEPP) triode power amp with an output stage much like conventional Output-TransformerLess (OTL) tube amplifier designs but with an impedance matching transformer instead of numerous power tubes in parallel to deliver adequate load current. The driver section...

The November/December 2018 issue of Nuts & Volts magazine has a lengthy feature article on a home brew THD analyzer that looks pretty easy to build. It includes the signal source, works at three different frequencies and uses an external AC voltmeter or scope for display.

I used to buy lots of components from a local military surplus dealer because it was a good way to stock up on high quality parts that would have otherwise been far beyond my budget at the time. I happened to use four 100R 2W(?) wirewound resistors from that old stock recently, and learned a...

Replacement turntable drive motors for these models have become nearly impossible to procure, so I decided to attempt replacement with a motor from the Beogram 2400 series. This item carries part number MHN-3P2RDS. Physical fitment isn't a problem, but hookup and tacho (FG) output frequency...

There have been many threads on this topic, so when I found an authoritative treatment in the Radio Designer's Handbook (Classic Edition), I decided it was worth quoting here verbatim: Temperature Rise This is dependent on the cooling area, the total loss and the ratio of iron to copper loss...

I needed a simple line amplifier for some chores around the shop, and decided to work up something of my own with cheap tubes that has very low output impedance and distortion. The gain target was 20dB. Cenote runs a pair of 6AU6s in standard pentode mode, but with relatively high operating...

I've been working my way through a forty-plus-year collection of iron-core transformers with a view to dis-accumulation, and stumbled across a bagful of these little one-inch cube size dudes. Feeding the 1K primary from a 1Vrms 50-ohm sinewave source and loading the full secondary with 1.2K, I...

So named by scientists, the Fangblenny is an extraordinary variant in a group of bashful little Australian reef fishes that wields a prodigious bite. Since this amplifier project is designed around a harmless little Australian speaker line matching transformer, yet poses a serious performance...

At Elektor magazine's website: https://www.elektormagazine.com/news/review-function-generator-in-the-pocket The squarewave ringing complaint is likely down to audio filter performance of the phone used for testing. Other phones might do better, but perfect squarewaves are unlikely from this...

This is such a frequent topic of discussion that I thought it would be worthwhile to post this item out of an EE rag dating 1959.

CatSkin grew out of a fascination with MCM’s very low cost 555-7125 “30W” speaker line matching transformer, which was used successfully as an audio output transformer in a couple of earlier push-pull triode power amp projects (Perveant & Bonseki). Because of its excellent high-frequency...

I was fooling around with one of my amplifier breadboards recently, trying to bring tube heater voltages on target with small amounts of series resistance, and discovered that shunting one of my resistors with a clip lead didn't change the heater voltage! So I tried another clip lead with 18 ga...

I've been playing with my new distortion analyzer and decided to test a few resistors. Raw data like this could be interesting to AKers, so here's a dump. The attached ZIP file has 23 PNG images taken with a very simple test fixture that puts a 10K test object (DUT) in series with a...

Not a proper review, but at least an interesting survey of low-cost instruments: http://wonderfulengineering.com/10-best-watt-meters/

Bonseki is a high-performance 20 watt per channel push-pull triode power amplifier that has been specifically designed to be accessible to tube DIYers on a budget. If there’s an amplifier food chain, then Bonseki’s natural prey would be conventional PP pentode creatures such as Magnavox console...

This project has origins tracing all the way back to 1978-1979, when I started thinking that I could improve tube power amplifier performance by inserting a direct-coupled solid-state grid drive stage. I built an all-solid-state drive circuit on a PCB and tested it in a couple of tube amp...

And screwed up right away, as usual: Kudos to those intrepid tube-o-philes who see what's wrong immediately! Cheers, Mike

I found an interesting iron core power transformer in a discarded computer UPS made by APC, model Back-UPS XS 900. This unit is rated by APC at 900VA, 9.2A/540W, and probably has squarewave output when operating on battery. It looks typical of many competitive products aimed at the consumer and...

There's a new outfit offering cloud-based schematic capture and other electronics design tools: Upverter http://www.upverter.com Their stuff is free to use if you don't need security, i.e. your work is published immediately. There's nothing to install; just use your web browser.

One of the reasons I invested in a good LCR bridge was to learn more about the non-spiritual characteristics of capacitors used in audio applications. In another thread, I offered to measure and publicly report on caps that are sent to me for analysis, without charge, as long as I don't get too...

A preliminary breadboard schematic is attached. I've decided to publish this project here before it's completed, for a couple of reasons: MCM Electronics is currently discounting the already-cheap OPTs, assuming that you receive MCM sale catalogs. Also, I feel that the design is due for a...

Over at EDN: http://www.edn.com/electronics-blogs/hackwire/4392164/The--slap-method--for-through-hole-rework?cid=Newsletter+-+EDN+Fun+Friday

This page offers a free software tool to help you suss out the current ratings of secondary windings on salvaged/surplus transformers: http://www.angelfire.com/electronic/funwithtubes/make_use.html You need some way to accurately measure low values of secondary DC resistance to make this...

Here's an interesting read: http://electronicdesign.com/article/analog-and-mixed-signal/-house-of-fire-firebottles-and-groove-tubes-versus-devices-that-find-their-origins-in-sand-part-1-?NL=ED-03&Issue=ED-03_20120524_ED-03_667&YM_RID=mikal@decadenet.com&YM_MID=1314629 Perhaps all those...

Here's a couple of simple DIY circuits that yield state-of-the-art distortion measurement resolution, albeit limited to a single test frequency: http://www.tmworld.com/article/521682-Low_distortion_oscillator_tests_measurement_circuits.php There's a nice little collection of references at the...