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Tuesday, April 21, 2009

Vintage sound amplification - Leak TL/10 amplifier and Varislope II Pre-Amp

Having made my first sale on New Zealand's internet trading system, TradeMe, my appetite is whet for further sales.

I sold a motor caravan in behalf of my father, and now I am preparing to sell what I thought was a derelict valve (tube) amplifier.

As I Googled away my singing practice time last Saturday, what follows is a brief summary of the remarkable story of the Leak TL/12 series of ground-breaking hi-fidelity valve amplifiers that I discovered....

Here is the basis for my first draft of an advertisement for TradeMe. Most of the content is drawn from the references presented at the end of the posting.

Vintage Audio - Leak "Point One" TL/10 Power Amplifier with matching Leak Varislope II Pre-Amplifier
According to Classique Sounds (Leicester UK) Leak equipment is on the "most wanted" list for vintage audiophiles. This Leak TL/10 valve amplifier and Varislope II pre-amp was produced in the early 1950s by H. J. Leak & Co. Ltd, Brunel Road, London. This type of equipment is appreciating in value as vintage collectibles

The equipment in this auction was purchased by my father second-hand circa 1962 in Wales, then brought to New Zealand where it was used until the early 1980s. Since then, the equipment has been stored inside in dry but dusty conditions and has probably not been used for 25+ years. Accordingly, relevant precautions must be taken before powering it up and leaving unattended. The gold "orange peel" enamel is slightly blemished in several areas (See photographs). There has been no attempt at modification or restoration since its purchase in 1962.

I have carefully removed the dust from the equipment and powered it up. The power amp is activated and all valves glow in both the pre-amp and power amp. The loudspeaker to which I connected the equipment very quietly hums at 50 Hz. Input signals applied to the several inputs (tape input, phono, aux) produce no result in either the loudspeaker, or the pre-amp tape output.

Sound quality
According to one seller on TradeMe: "Connected to good front end sources and efficient speakers these amps are still impressive sounding, and are appreciating in value as vintage collectibles." (8)

Specifications: "Point One" TL/10 Power Amplifier
10 Watts output.
Low total harmonic distortion: <= 0.1 per cent at rated output. Valves: EF86, 6SN7, 2 x KT61 in ultra-linear. Leak pamphlet states that the Brimar 6AG6G is an exact equivalent to the KT61. 5Z4 rectifier. Gold enamel finish. Mono only. Original UK purchase price (catologue new): "Point One" TL/10 power amplifier (17 guineas). (9) AT least four weeks wages of the time! Specifications: Leak "Varislope II"
First released: August 1954
This pre-amp features higher input sensitivities than previous Leak pre-amps, and has improved appearance.
Two EF86 valves are used, with a similar shunt feedback circuits as used in previous pre-amps.
The disc equalisations provided are: BRIT-78, BRIT-LP, COL-LP, RCA-Ortho, AES and NARTB.
Tuner, Tape, Mic and Auxilliary inputs are also provided.
Tape output.
Bass and treble are switch boost and cut, with the variable slope facility available for treble-cut.
Steel front panel finished in gold enamel.
Mono only.
Original UK purchase price (catologue new):16 pounds 16 shillings (16 Guineas)

Circuit topology
All Leak power amplifiers (Except Type 15) use the same basic circuit topology as the TL/12 The Topology comprises a first stage of voltage gain (with either triode or pentode), a triode long-tailed pair phase-splitter/driver stage, followed by an output stage (triode, tetrode, or ultra-linear) with cathode bias using separate cathode resistors" A discussion of the valves used in the TL/10, and substitutes is presented in (4, 10).

In 1949, Harold Leak demonstrated the foundation of the product line, the TL/12 "to amazed Americans" at the Audio Engineering Society exhibition that was held in New York. (9) The TL/10 was introduced as a lower cost alternative to the famous TL/12, but maintained the distortion rating of 0.1%.

The Leak "Point One" range of amplifiers was named for the low distortion figures achieved: the then "astonishingly low total harmonic distortion - at just 0.1 per cent for 15 Watts output" (5) The age of High Fidelity (hi-fi) had arrived!

H. J. Leak & Co Ltd were "Designers and Manufacturers of Specialised Electronic Instruments for the Communications Industries". Harold Leak, founder of the company, was particularly concerned that his designs were built to exacting standards and a high quality of finish. Unusually for equipment aimed at the domestic market, Leak amplifiers were built with component boards and cable looms. There are no printed circuits, transistors, or integrated chips. Capacitors were soldered into position with the value and rating markings visible, and resistors all had their tolerance bands at the same end. (1)

The TL series was "very well constructed, and featured a power supply with no electrolytic capacitors. The oil-filled paper capacitors used instead were costly but have a much longer life. Wiring standards were impeccable, and all transformers were finished for tropical operation."

The TL/10 followed the introduction of the TL/12 in 1948. The TL/12 was designed for "quantity production" premised on sales to three classes of users: Professional audio engineers, the non-technical music-lover or gramophile, and the knowledgeable amateur enthusiast (the "audio hobbyist" of the U.S.) who had previously built his own amplifiers for reasons of economy and/or personal satisfaction. For instance, the BBC placed large orders for the TL/12 to use as a component of its patented Monitor Loudspeaker. (9) The "Point One" series may well be an first example of what we now term a "prosumer" product: a high-end consumer product that matches professional performance and manufacturing standards.

The TL/10 amplifier was the first Leak amplifier to "incorporate the "ultra-linear" output stage configuration (popularised by Hafler and Keroes from the USA in the early 1950's, but earlier proposed by Blumlein). Many consider the TL/10 to be much under-rated these days. Leak certainly did not skimp on the ratings or size of the transformers, as they are identical in size to the TL/12 Plus (and Stereo 20 in the case of the output transformer)." (10)

In late 1951 H. J. Leak & Company published "a 28-page treatise explaining the history, concept, and design of the TL/12 amplifier and the associated RC/PA/U pre-amplifier. This pamphlet makes for fascinating reading for anyone interested in the history of the valve amplifier development during the "golden age" of audio (from the late 1940's to the early 1960's)." (10)

Recent auctions
Leak TL 12 "Mono" Power Amplifier complete with RC/PA pre amp - UK Ebay £UK 1000 as at 2 days before close (2)

Leak Stereo 20 Valve Amp for sale - TradeMe.co.nz - New Zealand Last bid: $900 (8). No pre-amp.

TL/10 Pair, £UK 450, UK, Jan 1999 (11)

TL/10 - one only, NEW in box. Bidding to US$530, but the reserve was not met.

TL/10 - one only, with Point One mono pre-amp. VGC. CA, USA, US$266, March1999.

2 x Varislope III pre-amps, filter knob missing, others knobs un-original, New York, USA, US$133 pair

Point One Stereo Pre amp - with Gold Anodised Facia, Australian Auction,Aug 1998, A$140

Varislope 2 Stereo Pre-amp, Grey/silver, lettering worn, knob center missing,Canada, US$46.50, Jan 1999

According to Classique Sounds (Leicester UK) Leak equipment is on the "most wanted" list for vintage audiophiles:
  • Leak Stereo 20
  • Leak TL10
  • Leak TL12/TL12+
  • Leak TL25
  • Leak TL50
  • Leak Stereo50/60 etc
"Current value of a single TL/12 in fine fettle is anywhere between £500 - £1,000; although recently (August 2006) I saw a matched pair with early serial numbers and minor modifications (RCA input and input level control) reach £2400 (US$4,500) on eBay. The immaculate unit with preamplifier (pictured at right) fetched £1480 in March 2006." (11)

Purchasers of this equipment are advised to have the equipment tested for safety prior to use or leaving unattended. Advice on history and restoration of Leak equipment is provided on the unofficial Leak Web site. The site is designed to "help encourage the restoration and maintenance of this wondeful audio equipment". (5) The site discusses resistors, capacitors, iron-cored components, connectors, and valves/tubes. Circuit diagrams are provided. (5)

Typical restorations include: "all capacitors and resistors replaced with good quality components, including film and foil coupling capacitors and the large dual section power filter capacitors. Replace input sockets and speaker terminals with better modern types." (8)

Service, user manuals and schematics, are also available from The Audio Circuit (TAC). (6)

An excellent series of photos illustrate and comment on the process of restoring a Leak Varislope. For instance, note the passion and perfection this restorer demonstrates: "Underneath as received. You don’t need to be an expert to spot that about a dozen components had already been changed here. Now, whilst there is no rule that says you can’t use radial and PCB mount components on a repair like this, I personally don’t think they look right. I decided to rip everything out and test/replace with the correct axial components." (7)

Restoration specialists
There are specialist restorers who rebuild Leak equipment. For instance, the restoration cost for a Leak Stereo 20 starts from £UK 199.00. I would expect the Point One restoration to be somewhat less expensive, since it is a mono rather than stereo device. (3) Of course, you may choose to acquire two Leak amplifiers so that you can create a stereo system.

There seem to be various alternative valves (tubes) that can be used to improve quality of performance. For instance: One restorer noted that: "All valves are good quality types, and are well matched and test to new spec or better. The input and phase splitter valves are Telefunken ECC83s; the output valves are Dutch made Philips ECC84s, and the rectifier is a Philips GZ34." (8). The unofficial Leak Web site also remarks on valve substitutions.

I have been advised of a local restoration specialist near my location in New Lynne. Accordingly, my next project is to get an estimate of the cost of restoration and/or just getting the fixed running in its "as is/where is" condition.

I make NO guarantees that this equipment will work. Furthermore, I make no guarantees that you will be able to locate replacement components. I have been advised that valves (tubes) are manufactured in Russia.

1. Leak TL/25 Plus audio amplifier and Varislope mono pre-amplifier - Object Wiki. (n.d.). . Retrieved April 18, 2009, from http://objectwiki.sciencemuseum.org.uk/wiki/Leak_TL/25_Plus_audio_amplifier_and_Varislope_mono_pre-amplifier.

2. Leak TL12 Point One Valve Power Amplifier + Preamp RCPA on eBay, also Separates, Audio, Vintage Electronics, Consumer Electronics (end time 20-Apr-09 10:39:50 BST). (n.d.). . Retrieved April 18, 2009, from http://cgi.ebay.co.uk/Leak-TL12-Point-One-Valve-Power-Amplifier-Preamp-RCPA_W0QQitemZ200330161874QQcategoryZ43804QQcmdZViewItem.

3. Classique Sounds (Leicester UK). (n.d.). . Retrieved April 18, 2009, from http://www.classiquesounds.co.uk/leak.htm.

4. Informazioni. (n.d.). . Retrieved April 18, 2009, from http://www.argaudio.it/index_file/Page492.htm.

5. H.J.Leak and Co. Ltd. - enthusiasts page. (n.d.). . Retrieved April 18, 2009, from http://44bx.com/leak/index.html.

6. Leak, Varislope 2 Stereo - manuals. (n.d.). . Retrieved April 18, 2009, from http://www.audiocircuit.com/index.php?c=LEA&m=Varislope%202%20Stereo.

7. Servicing of a Leak Varislope Stereo Hi-Fi Amplifier. (n.d.). . Retrieved April 18, 2009, from http://www.chambonino.com/work/hifi/hifi5.html.

8. Leak Stereo 20 Valve Amp for sale - TradeMe.co.nz - New Zealand. (n.d.). . Retrieved April 18, 2009, from http://www.trademe.co.nz/Electronics-photography/Home-audio/Vintage/auction-213553715.htm.

9. Leak TL/12 50'th Anniversary. (n.d.). . Retrieved April 18, 2009, from http://44bx.com/leak/TL12_50yrs.html.

10. Leak TL/10. (n.d.). . Retrieved April 18, 2009, from http://44bx.com/leak/TL10.html.

11. Leak TL/25 Plus - spot prices. (n.d.). . Retrieved April 18, 2009, from http://44bx.com/leak/prices.html.