Sequerra Model 1 FM Tuner
Webpage built 11/2007
Last updated 7/2017
Note: Additional info and photos of this tuner have been added on a separate webpage, click here for details.
This webpage is intended to provide resource materials for the Sequerra tuner for owners and anyone interested in this extraordinary tuner. I've included all materials I've collected over many years as well as a number of photos I've taken showing construction details. All the photos and scans here are available in higher resolution than initially shown - just click on the image to enlarge it. The content is arranged as follows:
Background and Reviews from industry publications
Sequerra Marketing Materials
Photos of the tuner, mostly internals
Maintenance, describing some parts that may be needed to maintain a Sequerra tuner
Modifications, with suggestions for upgrading its performance
Reference materials, with block diagrams and some partial schematics
Note that this page focuses on the original Sequerra Model 1 FM tuner, and although there were several subsequent versions made and sold by Day Sequerra, those are not the subject here. Information on the Day Sequerra tuners can be found on a companion webpage here.
Update 7/2017: Cabinet plans
Cabinets for the Sequerra tuner are very scarce. If you want one, i suggest contacting a local cabinetmaker/woodworking shop, or friend who is a woodworker to have one constructed in your choice of finish. I believe the originals were available in walnut and rosewood.
Above: Cabinet plans for the Sequerra Model One. Click to enlarge, then save locally and print.
UPDATE 6/2017: Misc. maintenance info thanks to Matt Kamna:
1. The ribbon cable discussed below in "Section 5, Modifications" is available in the correct 9 pin configuration. Mouser part number 538-25001-0902.
2. Replacement 20uf/250V caps are also available from Mouser, part number 75-TVA1508.
3. Matt suggests replacing the thermal grease under the 4 power supply pass transistors and the HP hexadecimal displays, as it dries out over the years.
4. As the incandescent display bulbs burn out, the voltage on the others goes up, shortening their life. Matt suggests replacing these lamps with LEDs (you'll need to add a series resistor) so they'll likely never need replacing again.
UPDATE 2/25/14: Updated Multiplex board info
Section 5: Modifications, subsection 2: Output Section Changes has been updated with suggested capacitor changes and info on the replacement of the ribbon cable which can come apart over time.
UPDATE 7/10/11: Repairs and maintenance
For any Sequerra owner needing repair or maintenance services, I highly recommend David Gill (of Gill Audio Design and Art Audio). He has the requisite knowledge base and documentation to successfully work on these complex tuners. His email is firstname.lastname@example.org.
UPDATE 7/10/11: De-emphasis changes for US vs Europe
I've had a few requests for information on changing the deemphasis circuit from 75us (US standard) to 50us (European standard) and vice versa. The following graphic, showing the front portion of the multiplex PCB (on the left side of the tuner), should be self explanatory.
UPDATE 4/09: CRT Replacement Info for the Day Sequerra FM Reference
David Gill (formerly of Gill Audio Design and Art Audio) has researched and documented information on the replacement of the CRT for the Day Sequerra FM Reference, but the info may be applicable to other Sequerra or Day Sequerra tuners as well. Read his very informative paper here. Highly recommended!
1. Background and Reviews
The Sequerra Model 1 was the first product of the Sequerra Company. Richard "Dick" Sequerra had been the primary designer of the equally famous Marantz 10B tuner a few years earlier. The Model 1 was as much a statement product as the 10B, but in solid state rather than tubes.
Work on the Model 1 was started in 1972, and it was produced for only a couple years starting in 1974. Based on a conversation I had with Dick Sequerra back in 1993, only about 1,400 units were produced, compared to about 8,000 Marantz 10Bs. (Note that other sources, such as here, indicate that only 5,500 10Bs were made.) It is interesting to note that one engineer at Sequerra indicated that 90% of sales were made to industry professionals, not audiophiles (see Boston Audio Society links below). The unit sold for $2,500 in 1974, equivalent to nearly $10,000 2007 dollars.
The Model 1 received rave reviews, (several included below), including from The Absolute Sound which ranked it in their "State-Of-The-Art" Editor's Choice category continuously from 1975 - 1978 (Vol 2, #6, again in #7, again in Vol 3, #9, and again in Vol 13, #11). Note that no other component stayed in their top category for that time period.
Above: March 1975 issue of Radio-Electronics magazine with Sequerra tuner featured on the cover. Click on image to enlarge. The entire review is available below in PDF format. This image cribbed from FMTunerInfo.com.
Sequerra Model 1 reviews available here in PDF format, in chronological order. Click on each to see the complete review:
Audio magazine review, August 1974.
2. Sequerra Marketing Materials
Early Sequerra brochure, 8 pages:
The following is an earlier flyer, indicated by the yellow lights on the sides of the face. Later units were white, a change apparently made by Fred Barrett when he took over the company after Dick's departure in 1975. For more details, see the Boston Audio Society articles in the LINKS section below. Click on any of these images to see a full-sized image, then you can right click to save yourself a copy if you'd like.
Above: Earlier Sequerra Model 1 brochure, front cover. Click to enlarge. Note there is no "S" logo on the power switch yet.
Above: Earlier Sequerra Model 1 brochure, page 2. Click to enlarge.
Above: Earlier Sequerra Model 1 brochure, page 3. Click to enlarge.
Above: Earlier Sequerra Model 1 brochure, page 4. Click to enlarge.
Above: Earlier Sequerra Model 1 brochure, page 5. Click to enlarge.
Above: Earlier Sequerra Model 1 brochure, page 6. Click to enlarge.
Above: Earlier Sequerra Model 1 brochure, page 7. Click to enlarge.
Above: Earlier Sequerra Model 1 brochure, rear cover. Click to enlarge. Note the front cover shows a silver faceplate tuner, and the rear cover a black faceplate.
Later Sequerra brochure, 8 pages:
Above: Later Sequerra Model 1 brochure, front cover. Click to enlarge.
Above: Later Sequerra Model 1 brochure, page 2. Click to enlarge.
Above: Later Sequerra Model 1 brochure, page 3. Click to enlarge.
Above: Later Sequerra Model 1 brochure, page 4. Click to enlarge.
Above: Later Sequerra Model 1 brochure, page 5. Click to enlarge.
Above: Later Sequerra Model 1 brochure, page 6. Click to enlarge.
Above: Later Sequerra Model 1 brochure, page 7. Click to enlarge.
Above: Later Sequerra Model 1 brochure, rear cover. Click to enlarge. This is actually the left side of the diagram continued on the front page, visible as a single piece with the brochure opened face down.
1977 Sequerra flyer, 2 pages:
Above: Marketing flyer dated 5-77, front. Click to enlarge.
Above: Marketing flyer dated 5-77, rear. Click to enlarge.
Most of the following photos are of the unit I worked on, and may not be representative of all Sequerra production.
Above: Sequerra with outer wrap-around cover in place. Click to enlarge.
Above: Logo and identifying information from rear panel, earlier version. Note (in the photo directly above this one) there is no name on front of the tuner, only the stylized letter "S" on the power switch.
Above: Later version of the rear panel. Note the tuner is now called "The Sequerra Model No. 1 Broadcast Monitor", and the Sequerra Company is listed as "A Member of the Barrett Group", and the address has changed.
Above: Front top view, cover removed. Click photo to enlarge. Note the CRT in the left center, the black encased power transformer to the right rear. The silver box above the tuning knob is a frequency counter for the LED display, and the circuit board to the left is for signal processing for the scope. The two blue capacitors to the left rear are part of the power supply.
Note that general layout of the chassis - with a large U-shaped frame containing various circuits - very reminiscent of the REL Precedent tuner. Here's a link to a photo of the REL on the great FMTunerInfo.com website.
Above: Bottom view, front is to the top. Click photo to enlarge. The PCB on the right is the power supply, and the blue cap on the far left is also part of the power supply.
Above: Left side view. Click photo to enlarge. This PCB is the multiplex section, and also contains the audio output circuitry on the far right (toward the front), which in this case has been slightly modified. More on that below.
Above: Right side view. Click photo to enlarge. This is the detector circuitry, encased in a stainless sub-chassis. And beneath that cover...
Above: The detector circuitry with the cover removed. Click photo to enlarge.
Above: Rear of chassis without covers. Click photo to enlarge. The left section is the 18 pole IF filter, and the right PCB is the RF front end. Each is encased in a separate stainless sub-chassis.
Above: rear view with covers showing connectors. Click photo to enlarge.
There are a number of parts in the Sequerra tuner that may periodically need replacing. These include:
1. Lamps. There are 4 types of lamps/displays:
Bulbs behind the yellow/white display windows: #1815 bulbs. These are commonly available. Note that I have tried a variety of LED replacements for the 1815, but none to date have worked well. Amber lamps I tried were much too dim, clear white showed hot spots, and diffuse white LEDs cast a very green light. Ultimately, I'm sticking with the original 1815 incandescent bulbs.
"Stereo" and "Megahertz" display indicators: #73 wedge base lamp. Also commonly available.
Smaller lamps behind indicator arrows and around CRT display are T 1-3/4 14.0 volt (AC) wire terminal lamps soldered to circuit boards, also commonly available. It looks like Chicago Miniature #2182 would work fine here. I would suggest replacing all of them if you go to the trouble of taking out the PCB to replace any one.
LED frequency display . These parts are no longer manufactured, but occasionally available online. These are Hewlett Packard parts, from the spec sheet: "solid state numeric and hexadecimal displays with on-board decoder/driver and memory". The part number is HP 5082-7302, and there are 4 of them (one for each digit) in the Sequerra. Failure modes include either a single digit being dimmer than others, or by individual dots on the display being dead. The datasheet for these displays is here.
2. The rubber belt connected to the tuning knob had cracked badly in the unit I worked on, and was replaced with a simple "O" ring from the local hardware store. The 1-5/8" Inside Diameter "O" ring matched exactly.
Above: Spare parts for Sequerra tuner, click to enlarge. Left to right: Tuning belt "O-ring", #1815 lamp, T 1-3/4 lamp, #73 lamp, HP LED display rear and front views.
3. The CRT is an Amperex D10-160GH. I don't know of any sources for this item. The Intensity setting for the scope will have an impact on CRT life, or at least affect burns on the screen. Hint: If you set the CRT intensity with the panel lamps in the DIM position so that it is barely visible, you can un-dim the panel lamps to tune your station, then dim the panel lights to preserve the CRT for most of the time it's on. In the reviews listed above, it was noted that the tuner was designed to automatically dim the display when it shrank to a dot, to protect the CRT from burn-in.
4. Fuses: These should not need replacement unless there is a problem. The correct value for the main fuse is 1Amp slow-blow for 110-120V mains, 0.5Amp for 220-240volt mains. Note that there is an additional 5Amp fuse inside the unit near the power supply board for the lamps.
I would also consider the electrolytic capacitor changes (described below in the Modifications section) as regular maintenance items - to be performed every quarter century or so.
Also in the next section is information on replacing the ribbon cable connecting the multiplexer board with the left front panel switching assembly, as that cable comes apart over time.
Although many would consider it heresy to modify such a collectable and classic tuner, there are a couple reasons in this case. First, and most importantly, the electrolytic capacitors will not last forever - typical life can range from 15 to potentially 30 years or longer, but we are now at the end of that range. So preventative maintenance of replacing the electrolytic capacitors in the power supply seems prudent, to prevent a failure that could destroy other (less easily replaced) components. I would suggest that all original parts that are removed should be kept together to pass along with the tuner to any future owners.
1. Capacitor changes:
There are 7 power supply electrolytic capacitors that I replaced. In order to keep the tuner as close to stock as possible, I replaced all of the caps with current production of the very same cap, which to my surprise, were all still in production. All of these changed caps look exactly like the originals except for newer date codes. The caps changes include:
Two 3,000uf/30volt Sprague 39D caps located on the top left part of the chassis. Note these are glued in place with silicone glue. The current production 39D still use the same blue plastic cover as the stock originals. The voltages across these caps was about 23VDC each.
One 8,000/15volt Sprague 39D cap located located on the bottom of the chassis. This cap is also glued in place with silicone glue. This cap has 10.5VDC across it.
Two 20uf/250volt Sprague 39D caps, located on the power supply PCB on the bottom of the chassis. Also replaced with new Sprague 39Ds. These caps have about 172VDC across each. Note that these two caps and the following pair are mounted on a double sided PCB. This board was made before plated thru-holes were common, and has a metal grommet connecting the traces on the two side. I was therefore able to replace these caps without removing the PCB, which is well integrated into the rest of the unit, making removal quite difficult.
Note: See "Update 6/2017" at the top of this page for additional info on the 20uf/250v caps.
Two 350uf/16volt caps located on the power supply PCB. The originals were Sprague 30D types, and although I couldn't find caps listed as 30D, I found Sprague TE caps with the same specs (105degree) and ordered them. It turns out that they in fact are also labeled 30D in addition to the "TE" label.
Note that the voltages across these last two caps (which are the regulated supply to audio output opamps, among other things) was +15.026 VDC and -14.984VDC. That puts them each within 0.2% of their target values more than 30 years after the tuner was built!
All of these replacement caps were bought from Mouser.com with the exception of the 20uf/250V 39D caps which Mouser doesn't stock, I had to get them directly from Vishay/Sprague.
2. Output section changes: Updated 2/2014
The audio output stage of the tuner has been criticized by some, including John Curl, who suggested that a competent modifier could improve it (link here to Curl's posting). When this particular tuner was purchased used & refurbished from Dick Sequerra in 1994, Dick upgraded the audio output section (details below). I made some additional minor changes to the audio output circuit, also discussed below. Dick Sequerra's 1994 modifications to this tuner included the following:
1. Replacement of the fixed and variable output RCA jacks with gold RCAs, shown below:
2. Replacement of the audio output ICs, originally a pair of LM301's. This IC is not well regarded for audio purposes (nor has it been for decades), and is easily surpassed in performance. Dick replaced it with a pair of MA332 ICs, which appear to be selected NE5534's, see John Curl's note here. In addition, Dick added an IC socket to facilitate changing the ICs in the future. IMPORTANT: There is a compensation capacitor, 15pf, just above each IC, from pin 1 to pin 8. If you replicate this change (either with this or different IC), that capacitor must be removed since it is only required for the LM301, not for more modern replacements.
Three various incarnations of the audio output stage are shown below: stock, Dick's modifications, and my changes.
Stock output section:
Above: Factory stock audio output section. Note the LM301 ICs and compensation caps immediately above each IC.
Sequerra modified output section:
Above: The audio section as modified by Dick Sequerra. Note the MA332 audio output ICs in the center. Just above each IC, you can just barely see the open holes that originally held 15pf compensation caps. No other changes here.
There were probably other changes that Dick made (in addition to verifying the alignment), but those are all that I am aware of.
My additional changes to the output section:
1.Replaced the MA332 ICs with OPA604s. These are generally regarded as quite musical and an improvement over the NE5534.
2. Replaced the 0.22uf output coupling caps with Soniccaps, 0.22uf/200V Gen 2. These are the same value but better audio quality than the originals, which were polyester Evox MMK types (0.22uf/100volt).
3. Replaced the 1uf coupling caps from the output filter section with Rifa PHE426 1uf/250V polypropylene, originals were also Evox MMK polyester.
All three of the above changes are shown and marked in the photo below.
Above: My modifications to the audio section, click to enlarge. The changes are the OPA604 ICs, the 0.22uf Sonicap coupling caps, and the 1.0uf Rifa coupling caps. Also shown here is the new ribbon cable in the lower right. Special thanks to David Gill for pointing out an error, since corrected, I made on a previous version of this photo.
Ribbon Cable: See "Update 6/2017" at the top of this page for additional info.
The ribbon cable connecting the multiplexer board with the right front panel switch assembly began to come apart in my unit. The cable can be seen in the lower right side of the three photos above. I replaced it with a 2" long ribbon cable from Mouser.com, part number 535-10-002-152FB. Looks like Mouser part number 538-25001-1002 is nearly identical. Note this replacement is a 10 conductor cable, so simply snip off one conductor to match the original 9 conductor cable. This new cable fits snugly into the gold receptacle on the multiplexer board, but must be soldered to the switch assembly PCB, as was the original. See photos below.
Above: original jumper cable, with plastic insulation coming apart.
Above: replacement jumper cable, soldered to the switch assembly PCB, awaiting insertion into the multiplexer board receptacle. Click to enlarge.
New Added 12/12/07: There was some discussion on two internet tuner groups of missing resistors in at least one Sequerra tuner, described in the links below. I am convinced, however, that this is not a problem common to all production, but here are the links for you to review:
Additionally, there is a related schematic and wiring layout here.
Note that the two missing resistors, listed by the author of the above posts as 100K, do show up on the schematic published in Radio-Electronics (reproduced below in the Reference Materials section). The RF amplifier of the Sequerra I worked on, as shown in the photos above, looks nothing like the diagram linked above either. See especially the Robert Dimpel response in the Audio Asylum thread above, who indicated that in in conversation with Tom Cadawas that this particular tuner was the very first Sequerra ever built. I can only conclude that that tuner was an early sample with an assembly error.
6. Reference Materials
For the complete Sequerra tuner manual in PDF format, Click Here.
Below: Simplified Block Diagram (from the early Sequerra brochure shown above). Click to enlarge:
Below: Front end schematic Diagram, from the Radio-Electronics review above. Click to enlarge:
Surprisingly, I have not found much information online about the Sequerra tuner. If you know of any related links, please pass them along to me an I'll add them here.
Dick Sequerra's website is here.
The DaySequerra website is here.
A May 1975 Boston Audio Society article on the history of the Sequerra Company around the time Dick Sequerra left the company is here. See Page 7.
A July 1975 Boston Audio Society article about a meeting with the new management of the Sequerra Company is here, see page 4.
Stereophile magazine's November 2002 article "40 years of Stereophile: The Hot 100 Products" is here, the Sequerra tuner is #66, tied with the McIntosh MR-78 - see page 3.
FMTunerInfo.com - THE resource for tuner information of the web. This links to their Sequerra info.
Mouser.com - for Sprague powers supply caps
Sonicraft.com - for Soniccap coupling caps